Merge lp:~georg-zotti/stellarium/gz_fix-ecliptic-obliquity into lp:stellarium

[gzotti]

This brings an important change in accuracy, fixing several questions about accuracy of simulation in antiquity. Please see branch description for details.

There are a few issues to be fixed as discussed in the last few weeks. Precession (coming here), deltaT once again (I suggest doing this next) and Nutation (IAU-2000A should replace the currently used old model from the 1980s). Accuracy gains/testing against solutions known to be accurate) is best done in this sequence. I left a few remarks and TODO notes in the code in places that should soon be fixed (IMHO these are things that should be done before 0.14 is prepared).

[lp:~georg-zotti/stellarium/gz_fix-ecliptic-obliquity]

7615. By gzotti on 2015-07-27

Added reference to README. A few docfixes and removed some excess comments.

[Alexander Wolf (alexwolf)]

Georg, are you can add unit tests for this feature? It should be helpful for checking accuracy and checking for correct for the code.

review: Needs Information

[Alexander Wolf (alexwolf)]

Oh! One important note - pole precision line is not a circle, it's spirale. Current implementation can confuse many peoples. I think this line may be implemented as line with some range of the dates, like orbits in Satellites plugin.

review: Needs Information

[Alexander Wolf (alexwolf)]

Revision 7610 contains the code:

oss << q_("Ecliptic obliquity (of date): %1").arg(StelUtils::radToDmsStr(ecl, true)) << "<br>";

which will be displayed when any object is selected.

But (!):
1) this line give info about current planet, where observer is located, not about the selected object!
2) Ecliptic obliquity for Sun is not have physical sense.

[Alexander Wolf (alexwolf)]

Revision 7612: I think short keys for add/subtract Julian century should be added. :)

[Alexander Wolf (alexwolf)]

Revision 7613: same problem as in revision 7610 - the planetocentric distance shows info not for the selected planet, what will be confused users.

[Alexander Wolf (alexwolf)]

I'm sorry, but notes from my last 3 comments should be fixed IMHO.

review: Needs Fixing

[gzotti (georg-zotti)]

> Revision 7610 contains the code:
>
> oss << q_("Ecliptic obliquity (of date): %1").arg(StelUtils::radToDmsStr(ecl,
> true)) << "<br>";
>
> which will be displayed when any object is selected.
>
> But (!):
> 1) this line give info about current planet, where observer is located, not
> about the selected object!
> 2) Ecliptic obliquity for Sun is not have physical sense.

"Ecliptic" is only Earth's orbital plane, there is no source or reason for confusion. But given the fact that we also don't show ecliptical grid of date if located on other planets, I will change to not show it if location is not on Earth.

[gzotti (georg-zotti)]

> Revision 7612: I think short keys for add/subtract Julian century should be
> added. :)

Yes, only in comparing the merge submission I have seen that Sidereal Year has vanished (?)
I would even like to have Sidereal, Tropical, Julian, and Anomalistic year! But I am easily running out of hotkeys! Whatever time jumps we decide upon for 0.14 I think we can add them just before release.

[Alexander Wolf (alexwolf)]

>"Ecliptic" is only Earth's orbital plane, there is no source or reason for confusion. But given the fact that we also don't show ecliptical grid of date if located on other planets, I will change to not show it if location is not on Earth.

Why? When we say "ecliptic" then we saying about Earth, it's typical, but other planets has "path of the Sun" too and other planet has ecliptic too ;)

[Alexander Wolf (alexwolf)]

> Yes, only in comparing the merge submission I have seen that Sidereal Year has vanished (?)

No, it exists. (Hint: http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/7734)

> I would even like to have Sidereal, Tropical, Julian, and Anomalistic year! But I am easily running out of hotkeys! Whatever time jumps we decide upon for 0.14 I think we can add them just before release.

What about filling feature request, because we can forget it?

[Alexander Wolf (alexwolf)]

Oops... Why "Ecliptic obliquity (of date)" string are ignores the option of settings for decimal format displaying? :)

[Alexander Wolf (alexwolf)]

Georg, please ignore my comment about precession :)

[gzotti (georg-zotti)]

> Revision 7613: same problem as in revision 7610 - the planetocentric distance
> shows info not for the selected planet, what will be confused users.

Oh yes, it does. It should display how many km observer is located away from his planet's center.

But ... argh - something is wrong for off-earth sites. Must fix that, sure. (Last-minute thing I wanted to put in here, only tested for Earth. *-(

[gzotti (georg-zotti)]

> >"Ecliptic" is only Earth's orbital plane, there is no source or reason for
> confusion. But given the fact that we also don't show ecliptical grid of date
> if located on other planets, I will change to not show it if location is not
> on Earth.
>
> Why? When we say "ecliptic" then we saying about Earth, it's typical, but
> other planets has "path of the Sun" too and other planet has ecliptic too ;)

No, "The Ecliptic" is specifically the projection of Earth's instantaneous orbital plane onto the celestial sphere, appearing as great circle.

Other planets' orbital planes are just called "orbital planes", and Stellarium so far never made an attempt to show other planets' orbital planes (although it would certainly be nice for astronaut training...). "Ecliptic" is particularly Earth-related, like "The Moon" is only our Earth's moon.

There is apparently some widespread idea that Earth's orbital plane is stable in VSOP coordinates. It is not the case, as we can see here and now! VSOP has the J2000.0 ecliptical plane as their XY-plane, which Stellarium can show as "Ecliptic of J2000.0". But Earth's orbit is wandering around a bit, which is called the Precession of the Ecliptic (Earlier name: "planetary precession", but in the post-2000 literature authors preferred "Precession of the Ecliptic").

[gzotti (georg-zotti)]

> Oops... Why "Ecliptic obliquity (of date)" string are ignores the option of
> settings for decimal format displaying? :)

fixed in r7616, thanks.

[gzotti (georg-zotti)]

> Oh! One important note - pole precision line is not a circle, it's spirale.
> Current implementation can confuse many peoples. I think this line may be
> implemented as line with some range of the dates, like orbits in Satellites
> plugin.

Yes it's a spiral. But what I show here is the "instantaneous circle" which at least visualizes the concept. Avid observers will note that stars orbiting the instantaneous pole of ecliptic of date next to this circle will intersect the circle, and that Polaris will have a different polar distance next time it is pole star. I think this is perfectly enough as visualisation for now.

When the feature request "orbit with labeled date marks" has been implemented, maybe someone can also implement the spiral with date labels then?

In these time ranges (tens of thousands of years) it's sad to see that VSOP87 only covers less than 1/2 cycle... But I have never seen the answer to "what happens outside -4000...+8000" as clearly.

DE431 should show a bit more than 1 cycle, at least.

[gzotti (georg-zotti)]

> Georg, please ignore my comment about precession :)

I hope you mean ignoring the spiral request? I have no plan to implement any spiral path before December (if at all), there are really more urgent things (e.g. moon rotation!) and I do also not have infinite time, sorry.

[gzotti (georg-zotti)]

> > Revision 7613: same problem as in revision 7610 - the planetocentric
> distance
> > shows info not for the selected planet, what will be confused users.
>
> Oh yes, it does. It should display how many km observer is located away from
> his planet's center.
>
> But ... argh - something is wrong for off-earth sites. Must fix that, sure.
> (Last-minute thing I wanted to put in here, only tested for Earth. *-(

OK, fixed that in r7617.

This value may actually only be useful while testing. Again, it does not give distance to observed object, but to the center of the planet you are standing on. (Needed for topocentric correction, which used purely-spherical planets until now.)

[lp:~georg-zotti/stellarium/gz_fix-ecliptic-obliquity]

7616. By gzotti on 2015-07-27

show ecliptic obliquity also with non-decimal string

7617. By gzotti on 2015-07-27

ensure getDistanceFromCenter() does not cause problems while observing from SpaceShipObserver

[Alexander Wolf (alexwolf)]

OK, I think ecliptic obliquity and XYZ should display for Earth only and she should not mixed with other data for the chosen planets. What think about adding "For Earth:" line after info (after the one empty line) and put ecliptic obliquity and XYZ data after it.

The question for info with the planetocentric distance is more difficult here, because this infobox should not mixed with data about chosen planet too. But this data available for all planets in general. I think I can propose compromise for visualization of this data - add the planetocentric distance info as tooltip for height data on bottom toolbar.

[Alexander Wolf (alexwolf)]

I guess we can open question about implementation rendering line of precession after introducing DE4x parts.

[lp:~georg-zotti/stellarium/gz_fix-ecliptic-obliquity]

7618. By gzotti on 2015-07-28

added unit tests (themselves untested, TBD on other platform)

7619. By gzotti on 2015-07-28

added test case files

7620. By gzotti on 2015-07-28

commented away XYZ and planetocentric observer coordinates

7621. By gzotti on 2015-07-28

harmonized visible (grid) and displayed ecliptical coordinates for non-earth locations. We cannot compute orbit-related coordinates for other planets yet :-(

[gzotti (georg-zotti)]

> OK, I think ecliptic obliquity and XYZ should display for Earth only and she
> should not mixed with other data for the chosen planets. What think about
> adding "For Earth:" line after info (after the one empty line) and put
> ecliptic obliquity and XYZ data after it.

Given that nobody outside our development team thinks that "Ecliptic" does not refer to the Earth only, I see no need to annotate "Ecliptic" with "Earth".

By the way, the "ecliptical coordinates" in the infostring are totally nonsense for observer locations outside earth. You would have to first find orbital plane for the planet, and then the "spring point" (ascending node between orbital plane and planet equator). The situation found here were in principle terrestrial ecliptical coordinates with different obliquity, that's nonsense. I now have changed this, for non-terrestrial observers, to

*) show "ecliptical coordinates J2000" referring to earth's orbital plane of J2000.
   The displayed coordinates fit to the displayed ecliptical grid of J2000.
*) Disable display of ecliptical coordinates of date because they were wrong.
*) Disable display of "Ecliptic obliquity" for non-earth observers to avoid confusion.

If we want to display "axis inclination to planet's orbit" or (90-Planet.getRotObliquity(JDE)), this may be a nice extra information.

Also XYZ is mostly here for testing, but it should show selected object's position in "parentocentric" XYZ coordinates (i.e., for moons we have the respective planets as zero). I have commented it away for your comfort. Please do not delete the lines, though, I think it can be helpful when integrating DE431 which have to be rotated into VSOP87 reference frame.

> The question for info with the planetocentric distance is more difficult here,
> because this infobox should not mixed with data about chosen planet too. But
> this data available for all planets in general. I think I can propose
> compromise for visualization of this data - add the planetocentric distance
> info as tooltip for height data on bottom toolbar.

Also here I just wanted a quick view while I move latitude with the location panel open, and not just qDebug() lines in the logfile. The current location was admittedly not good, but this is an intermediate state, not polished. If you can make a tooltip from that, it's fine.

r7621 has the latest changes. I now move to Linux for testing the unit test...

[lp:~georg-zotti/stellarium/gz_fix-ecliptic-obliquity]

7622. By gzotti on 2015-07-28

avoid debug print also in "regular" debug builds.

7623. By gzotti on 2015-07-28

added toString() functions for matrices. Clarified (unused) upper3x3().

7624. By gzotti on 2015-07-28

First unit test for precession complete.

7625. By gzotti on 2015-07-28

added another test

[gzotti (georg-zotti)]

> Georg, are you can add unit tests for this feature? It should be helpful for
> checking accuracy and checking for correct for the code.

Alright, a few unit tests against the numerical example given in the paper are completed (r7625). There was even a minus missing in the (otherwise unused) reference solution :-P
Not sure about how the unit tests are used in an automatic workflow, are debug messages allowed? I leave them in but commented away, for further development.

Alex, I hope this completes the package of your requests. This branch does not care for other planets' orbital planes which were never properly handled by now, only applications in terrestrial history will see a benefit.

Again, this is Step 1 of 3 to be done in the next few weeks to solve several critical questions by historically inclined audience. #2 shall be correct application of DeltaT, and #3 shall bring in Nutation with the IAU-2000A model fitting to the 2006 precession of which this Vondrak model is a compatible, extended version.

Anything missing?

review: Needs Resubmitting

[Alexander Wolf (alexwolf)]

>Not sure about how the unit tests are used in an automatic workflow, are debug messages allowed?

No.

review: Approve

=== modified file 'README'
--- README	2015-03-23 00:02:31 +0000
+++ README	2015-07-28 19:18:20 +0000
@@ -207,6 +207,10 @@
 		[19] "Astronomy on the Personal Computer" by O. Montenbruck & T. Pfleger (4nd ed., 2000)
 		[20] "Calendrical Calculations" by E. M. Reingold & N. Dershowitz (2nd ed., 2001)
 		[21] DeltaT webpage by V. Reijs: http://www.iol.ie/~geniet/eng/DeltaTeval.htm
+	1.5 An accurate long-time precession model compatible with P03:
+		J. Vondrak, N. Capitaine, P. Wallace: New precession expressions, valid for long time intervals.
+		Astronomy&Astrophysics 534, A22 (2011); DOI: 10.1051/0004-6361/201117274
+
 
 2. Included source code
 	2.1 Some computation of the sideral time (sidereal_time.h/c) and pluto
@@ -252,7 +256,7 @@
 		-) compute nr_of_measurements = the number of valid b,v,r values
 		-) throw away or keep stars (depending on magnitude,
 		   nr_of_measurements, combination of flags, tycho2 number)
-		-) add all stars from hiparcos (incl. component solutions), and
+		-) add all stars from Hipparcos (incl. component solutions), and
 		   tycho2+1st supplement
 		-) reorganize the stars in several brigthness levels and
 		   triangular zones according to position and magnitude

=== modified file 'data/default_config.ini.cmake'
--- data/default_config.ini.cmake	2015-06-19 18:02:55 +0000
+++ data/default_config.ini.cmake	2015-07-28 19:18:20 +0000
@@ -113,7 +113,6 @@
 #base_font_name                      = DejaVu Sans
 mouse_cursor_timeout                = 10
 flag_mouse_cursor_timeout           = false
-day_key_mode                        = calendar
 selected_object_info                = all
 auto_hide_horizontal_toolbar        = true
 auto_hide_vertical_toolbar          = true
@@ -124,13 +123,27 @@
 gui_base_color                      = 0.5,0.5,0.7
 gui_text_color                      = 0.8,0.9,0.9
 azimuthal_color                     = 0.3,0.2,0.1
-equatorial_color                    = 0.1,0.2,0.3
-equatorial_J2000_color              = 0.1,0.3,0.4
+daylight_text_color                 = 0.0,0.0,0.0
+# 
+#equatorial_color                    = 0.1,0.2,0.3
+#equatorial_J2000_color              = 0.1,0.3,0.4
+#equator_color                       = 0.2,0.2,0.6
+#ecliptic_color                      = 0.6,0.2,0.2
+#ecliptic_J2000_color                = 0.3,0.3,0.1
+# GZ instead: Note -al colors go to the grids.
+ecliptic_J2000_color                   = 0.7,0.2,0.2
+ecliptic_color                         = 0.9,0.6,0.2
+ecliptical_J2000_color                 = 0.4,0.1,0.1
+ecliptical_color                       = 0.6,0.3,0.1
+# default: same as ecliptic_color
+precession_circle_color                = 0.9,0.6,0.2
+equator_J2000_color                    = 0.2,0.2,0.6
+equator_color                          = 0.3,0.5,1.0
+equatorial_J2000_color                 = 0.1,0.1,0.5
+equatorial_color                       = 0.2,0.3,0.8
+#
 galactic_color                      = 0.0,0.3,0.2
 galactic_equator_color              = 0.5,0.3,0.1
-equator_color                       = 0.2,0.2,0.6
-ecliptic_color                      = 0.6,0.2,0.2
-ecliptic_J2000_color                = 0.3,0.3,0.1
 meridian_color                      = 0.2,0.6,0.2
 longitude_color                     = 0.2,0.4,0.4
 horizon_color                       = 0.2,0.6,0.2
@@ -207,11 +220,14 @@
 flag_azimuthal_grid                 = false
 flag_equatorial_grid                = false
 flag_equatorial_J2000_grid          = false
+flag_ecliptic_grid                  = false
 flag_ecliptic_J2000_grid            = false
 flag_galactic_grid                  = false
 flag_galactic_equator_line          = false
 flag_equator_line                   = false
+flag_equator_J2000_line             = false
 flag_ecliptic_line                  = false
+flag_ecliptic__J2000_line           = false
 flag_meridian_line                  = false
 flag_longitude_line                 = false
 flag_horizon_line                   = false

=== modified file 'src/CMakeLists.txt'
--- src/CMakeLists.txt	2015-06-13 20:19:16 +0000
+++ src/CMakeLists.txt	2015-07-28 19:18:20 +0000
@@ -174,6 +174,8 @@
 	core/planetsephems/marssat.h
 	core/planetsephems/pluto.c
 	core/planetsephems/pluto.h
+	core/planetsephems/precession.c
+	core/planetsephems/precession.h
 	core/planetsephems/sidereal_time.c
 	core/planetsephems/sidereal_time.h
 	core/planetsephems/stellplanet.c
@@ -620,6 +622,23 @@
 ADD_DEPENDENCIES(buildTests testRefraction)
 ADD_TEST(testRefraction)
 
+SET(tests_testPrecession_SRCS
+        tests/testPrecession.hpp
+        tests/testPrecession.cpp
+        core/planetsephems/precession.h
+        core/planetsephems/precession.c
+        core/StelUtils.hpp
+        core/StelUtils.cpp)
+IF(WIN32)
+        # StelUtils required zlib sources
+        SET(tests_testPrecession_SRCS ${tests_testPrecession_SRCS} ${zlib_SRCS})
+ENDIF()
+ADD_EXECUTABLE(testPrecession EXCLUDE_FROM_ALL ${tests_testPrecession_SRCS})
+QT5_USE_MODULES(testPrecession Core Gui Widgets Script Declarative Test)
+TARGET_LINK_LIBRARIES(testPrecession ${extLinkerOptionTest})
+ADD_DEPENDENCIES(buildTests testPrecession)
+ADD_TEST(testPrecession)
+
 ADD_CUSTOM_TARGET(tests COMMENT "Run the Stellarium unit tests")
 FOREACH(NAME ${STELLARIUM_TESTS})
 	IF(MSVC)

=== modified file 'src/core/StelCore.cpp'
--- src/core/StelCore.cpp	2015-07-25 17:05:44 +0000
+++ src/core/StelCore.cpp	2015-07-28 19:18:20 +0000
@@ -37,6 +37,7 @@
 #include "LandscapeMgr.hpp"
 #include "StelTranslator.hpp"
 #include "StelActionMgr.hpp"
+#include "precession.h"
 
 #include <QSettings>
 #include <QDebug>
@@ -311,10 +312,12 @@
 	{
 		case FrameAltAz:
 			return getProjection(getAltAzModelViewTransform(refractionMode));
-		case FrameHeliocentricEcliptic:
+		case FrameHeliocentricEclipticJ2000:
 			return getProjection(getHeliocentricEclipticModelViewTransform(refractionMode));
-		case FrameObservercentricEcliptic:
-			return getProjection(getObservercentricEclipticModelViewTransform(refractionMode));
+		case FrameObservercentricEclipticJ2000:
+			return getProjection(getObservercentricEclipticJ2000ModelViewTransform(refractionMode));
+		case FrameObservercentricEclipticOfDate:
+			return getProjection(getObservercentricEclipticOfDateModelViewTransform(refractionMode));
 		case FrameEquinoxEqu:
 			return getProjection(getEquinoxEquModelViewTransform(refractionMode));
 		case FrameJ2000:
@@ -635,9 +638,9 @@
 Vec3d StelCore::heliocentricEclipticToAltAz(const Vec3d& v, RefractionMode refMode) const
 {
 	if (refMode==RefractionOff || skyDrawer==NULL || (refMode==RefractionAuto && skyDrawer->getFlagHasAtmosphere()==false))
-		return matHeliocentricEclipticToAltAz*v;
+		return matHeliocentricEclipticJ2000ToAltAz*v;
 	Vec3d r(v);
-	r.transfo4d(matHeliocentricEclipticToAltAz);
+	r.transfo4d(matHeliocentricEclipticJ2000ToAltAz);
 	skyDrawer->getRefraction().forward(r);
 	return r;
 }
@@ -648,26 +651,29 @@
 	return matHeliocentricEclipticToEquinoxEqu*v;
 }
 
+/*
 //! Transform vector from heliocentric coordinate to false equatorial : equatorial
-//! coordinate but centered on the observer position (usefull for objects close to earth)
+//! coordinate but centered on the observer position (useful for objects close to earth)
+//! Unused as of V0.13
 Vec3d StelCore::heliocentricEclipticToEarthPosEquinoxEqu(const Vec3d& v) const
 {
 	return matAltAzToEquinoxEqu*matHeliocentricEclipticToAltAz*v;
 }
+*/
 
 StelProjector::ModelViewTranformP StelCore::getHeliocentricEclipticModelViewTransform(RefractionMode refMode) const
 {
 	if (refMode==RefractionOff || skyDrawer==NULL || (refMode==RefractionAuto && skyDrawer->getFlagHasAtmosphere()==false))
-		return StelProjector::ModelViewTranformP(new StelProjector::Mat4dTransform(matAltAzModelView*matHeliocentricEclipticToAltAz));
+		return StelProjector::ModelViewTranformP(new StelProjector::Mat4dTransform(matAltAzModelView*matHeliocentricEclipticJ2000ToAltAz));
 	Refraction* refr = new Refraction(skyDrawer->getRefraction());
 	// The pretransform matrix will convert from input coordinates to AltAz needed by the refraction function.
-	refr->setPreTransfoMat(matHeliocentricEclipticToAltAz);
+	refr->setPreTransfoMat(matHeliocentricEclipticJ2000ToAltAz);
 	refr->setPostTransfoMat(matAltAzModelView);
 	return StelProjector::ModelViewTranformP(refr);
 }
 
-//! Get the modelview matrix for observer-centric ecliptic (Vsop87) drawing
-StelProjector::ModelViewTranformP StelCore::getObservercentricEclipticModelViewTransform(RefractionMode refMode) const
+//! Get the modelview matrix for observer-centric ecliptic J2000 (Vsop87A) drawing
+StelProjector::ModelViewTranformP StelCore::getObservercentricEclipticJ2000ModelViewTransform(RefractionMode refMode) const
 {
 	if (refMode==RefractionOff || skyDrawer==NULL || (refMode==RefractionAuto && skyDrawer->getFlagHasAtmosphere()==false))
 		return StelProjector::ModelViewTranformP(new StelProjector::Mat4dTransform(matAltAzModelView*matJ2000ToAltAz*matVsop87ToJ2000));
@@ -678,6 +684,19 @@
 	return StelProjector::ModelViewTranformP(refr);
 }
 
+//! Get the modelview matrix for observer-centric ecliptic-of-date drawing
+StelProjector::ModelViewTranformP StelCore::getObservercentricEclipticOfDateModelViewTransform(RefractionMode refMode) const
+{
+	double eps_A=getPrecessionAngleVondrakCurrentEpsilonA();
+	if (refMode==RefractionOff || skyDrawer==NULL || (refMode==RefractionAuto && skyDrawer->getFlagHasAtmosphere()==false))
+		return StelProjector::ModelViewTranformP(new StelProjector::Mat4dTransform(matAltAzModelView*matEquinoxEquToAltAz* Mat4d::xrotation(eps_A)));
+	Refraction* refr = new Refraction(skyDrawer->getRefraction());
+	// The pretransform matrix will convert from input coordinates to AltAz needed by the refraction function.
+	refr->setPreTransfoMat(matEquinoxEquToAltAz* Mat4d::xrotation(eps_A));
+	refr->setPostTransfoMat(matAltAzModelView);
+	return StelProjector::ModelViewTranformP(refr);
+}
+
 //! Get the modelview matrix for observer-centric equatorial at equinox drawing
 StelProjector::ModelViewTranformP StelCore::getEquinoxEquModelViewTransform(RefractionMode refMode) const
 {
@@ -729,31 +748,52 @@
 	return StelProjector::ModelViewTranformP(refr);
 }
 
+// GZ: One of the most important functions, totally void of doc. :-(
+// called in update() (for every frame)
 void StelCore::updateTransformMatrices()
 {
 	matAltAzToEquinoxEqu = position->getRotAltAzToEquatorial(JDay);
 	matEquinoxEquToAltAz = matAltAzToEquinoxEqu.transpose();
 
+	// multiply static J2000 earth axis tilt (eclipticalJ2000<->equatorialJ2000)
+	// in effect, this matrix transforms from VSOP87 ecliptical J2000 to planet-based equatorial coordinates.
+	// For earth, matJ2000ToEquinoxEqu is the precession matrix.
+	// TODO: rename matEquinoxEquToJ2000 to matEquinoxEquDateToJ2000
 	matEquinoxEquToJ2000 = matVsop87ToJ2000 * position->getRotEquatorialToVsop87();
 	matJ2000ToEquinoxEqu = matEquinoxEquToJ2000.transpose();
 	matJ2000ToAltAz = matEquinoxEquToAltAz*matJ2000ToEquinoxEqu;
 
 	matHeliocentricEclipticToEquinoxEqu = matJ2000ToEquinoxEqu * matVsop87ToJ2000 * Mat4d::translation(-position->getCenterVsop87Pos());
 
-	// These two next have to take into account the position of the observer on the earth
+	// These two next have to take into account the position of the observer on the earth/planet of observation.
+	// GZ tmp could be called matAltAzToVsop87
 	Mat4d tmp = matJ2000ToVsop87 * matEquinoxEquToJ2000 * matAltAzToEquinoxEqu;
 
-	matAltAzToHeliocentricEcliptic =  Mat4d::translation(position->getCenterVsop87Pos()) * tmp *
+	// TODO: getDistanceFromCenter assumes spherical planets. Use rectangular coordinates for observer!
+	matAltAzToHeliocentricEclipticJ2000 =  Mat4d::translation(position->getCenterVsop87Pos()) * tmp *
 						  Mat4d::translation(Vec3d(0.,0., position->getDistanceFromCenter()));
 
-	matHeliocentricEclipticToAltAz =  Mat4d::translation(Vec3d(0.,0.,-position->getDistanceFromCenter())) * tmp.transpose() *
+	matHeliocentricEclipticJ2000ToAltAz =  Mat4d::translation(Vec3d(0.,0.,-position->getDistanceFromCenter())) * tmp.transpose() *
 						  Mat4d::translation(-position->getCenterVsop87Pos());
+
+
+//	Given that ecliptic of date is apparently not used any longer as reference plane for astronomical computations, it is enough to display it.
+//	This half-finished block of comments can the likely go away for V0.14. Else, do we have use for carrying the extra matrices with us? Then complete this:
+//	// GZ Finally, new: rotation of the ecliptic of date. Not sure which direction, though...
+//	double epsilon_A, chi_A, omega_A, psi_A;
+//	// MAKE SURE JDay IS TT!!!
+//	getPrecessionAnglesVondrak(JDay, &epsilon_A, &chi_A, &omega_A, &psi_A);
+//	//matVsop87ToEclOfDate= Mat4d::xrotation(epsilon_A)*Mat4d::zrotation(chi_A)*Mat4d::xrotation(-omega_A)*Mat4d::zrotation(-psi_A);
+//	matVsop87ToEclOfDate= Mat4d::xrotation(epsilon_A)*Mat4d::zrotation(chi_A)*Mat4d::xrotation(-23.4392803055555555556*(M_PI/180));
+//	matEclOfDateToVsop87=matVsop87ToEclOfDate.transpose();
+//	//matEclOfDateToVsop87= Mat4d::xrotation(epsilon_A)*Mat4d::zrotation(chi_A)*Mat4d::xrotation(-omega_A)*Mat4d::zrotation(-psi_A);
+//	//matVsop87ToEclOfDate=matVsop87ToEclOfDate.transpose();
 }
 
 // Return the observer heliocentric position
 Vec3d StelCore::getObserverHeliocentricEclipticPos() const
 {
-	return Vec3d(matAltAzToHeliocentricEcliptic[12], matAltAzToHeliocentricEcliptic[13], matAltAzToHeliocentricEcliptic[14]);
+	return Vec3d(matAltAzToHeliocentricEclipticJ2000[12], matAltAzToHeliocentricEclipticJ2000[13], matAltAzToHeliocentricEclipticJ2000[14]);
 }
 
 // Set the location to use by default at startup
@@ -905,6 +945,11 @@
 	return position->getHomePlanet();
 }
 
+const StelObserver *StelCore::getCurrentObserver() const
+{
+	return position;
+}
+
 // Smoothly move the observer to the given location
 void StelCore::moveObserverTo(const StelLocation& target, double duration, double durationIfPlanetChange)
 {
@@ -1045,6 +1090,16 @@
 	addSolarDays(365.242190419);
 }
 
+void StelCore::addTropicalCentury()
+{
+	addSolarDays(36524.21897);
+}
+
+void StelCore::addJulianCentury()
+{
+	addSolarDays(36525.0);
+}
+
 void StelCore::subtractHour()
 {
 	addSolarDays(-JD_HOUR);
@@ -1105,6 +1160,16 @@
 	addSolarDays(-365.242190419);
 }
 
+void StelCore::subtractTropicalCentury()
+{
+	addSolarDays(-36524.21897);
+}
+
+void StelCore::subtractJulianCentury()
+{
+	addSolarDays(-36525.0);
+}
+
 void StelCore::addSolarDays(double d)
 {
 	const PlanetP& home = position->getHomePlanet();
@@ -1717,10 +1782,12 @@
 	return QString(" %1").arg(validRange);
 }
 
+// return if sky plus atmosphere is bright enough from sunlight so that e.g. screen labels should be rendered dark.
+// Could be renamed to isBrightDaylight()
 bool StelCore::isDay() const
 {
 	const Vec3d& sunPos = GETSTELMODULE(SolarSystem)->getSun()->getAltAzPosGeometric(this);
-	return sunPos[2] > -0.12; // Nautical twilight
+	return sunPos[2] > -0.12; // Nautical twilight (0.12 > sin (6 deg),
 }
 
 double StelCore::getCurrentEpoch() const

=== modified file 'src/core/StelCore.hpp'
--- src/core/StelCore.hpp	2015-07-08 10:37:11 +0000
+++ src/core/StelCore.hpp	2015-07-28 19:18:20 +0000
@@ -1,6 +1,7 @@
 /*
  * Copyright (C) 2003 Fabien Chereau
  * Copyright (C) 2012 Matthew Gates
+ * Copyright (C) 2015 Georg Zotti (Precession fixes)
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -38,11 +39,11 @@
 //! Main class for Stellarium core processing.
 //! This class provides services like management of sky projections,
 //! tone conversion, or reference frame conversion. It is used by the
-//! various StelModules to update and display themself.
+//! various StelModules to update and display themselves.
 //! There is currently only one StelCore instance in Stellarium, but
 //! in the future they may be more, allowing for example to display
 //! several independent views of the sky at the same time.
-//! @author Fabien Chereau
+//! @author Fabien Chereau, Matthew Gates, Georg Zotti
 class StelCore : public QObject
 {
 	Q_OBJECT
@@ -56,15 +57,17 @@
 	//! Supported reference frame types
 	enum FrameType
 	{
-		FrameUninitialized,		//!< Reference frame is not set (FMajerech: Added to avoid condition on uninitialized value in StelSkyLayerMgr::draw())
-		FrameAltAz,			//!< Altazimuthal reference frame centered on observer.
-		FrameHeliocentricEcliptic,	//!< Ecliptic reference frame centered on the Sun
-		FrameObservercentricEcliptic,	//!< Ecliptic reference frame centered on the Observer
-		FrameEquinoxEqu,		//!< Equatorial reference frame at the current equinox centered on the observer.
-						//! The north pole follows the precession of the planet on which the observer is located.
-		FrameJ2000,			//!< Equatorial reference frame at the J2000 equinox centered on the observer.
-						//! This is also the ICRS reference frame.
-		FrameGalactic			//! Galactic reference frame centered on observer.
+		FrameUninitialized,			//!< Reference frame is not set (FMajerech: Added to avoid condition on uninitialized value in StelSkyLayerMgr::draw())
+		FrameAltAz,				//!< Altazimuthal reference frame centered on observer.
+		FrameHeliocentricEclipticJ2000,		//!< Fixed-ecliptic reference frame centered on the Sun. GZ: This is J2000 ecliptical / almost VSOP87.
+		FrameObservercentricEclipticJ2000,	//!< Fixed-ecliptic reference frame centered on the Observer. GZ: was ObservercentricEcliptic, but renamed because it is Ecliptic of J2000!
+		FrameObservercentricEclipticOfDate,	//!< Moving ecliptic reference frame centered on the Observer. GZ new for V0.14: Ecliptic of date, i.e. includes the precession of the ecliptic.
+		FrameEquinoxEqu,			//!< Equatorial reference frame at the current equinox centered on the observer.
+							//!< The north pole follows the precession of the planet on which the observer is located.
+							//!< TBD: To be Corrected for V0.14 to really properly reflect ecliptical motion and precession (Vondrak 2011 model)
+		FrameJ2000,				//!< Equatorial reference frame at the J2000 equinox centered on the observer.
+							//!< This is also the ICRS reference frame.
+		FrameGalactic				//!< Galactic reference frame centered on observer.
 	};
 
 	//! @enum ProjectionType
@@ -150,11 +153,11 @@
 	//! only for 2d painting
 	StelProjectorP getProjection2d() const;
 
-	//! Get a new instance of projector using a modelview transformation corresponding to the the given frame.
+	//! Get a new instance of projector using a modelview transformation corresponding to the given frame.
 	//! If not specified the refraction effect is included if atmosphere is on.
 	StelProjectorP getProjection(FrameType frameType, RefractionMode refractionMode=RefractionAuto) const;
 
-	//! Get a new instance of projector using the given modelview transformatione.
+	//! Get a new instance of projector using the given modelview transformation.
 	//! If not specified the projection used is the one currently used as default.
 	StelProjectorP getProjection(StelProjector::ModelViewTranformP modelViewTransform, ProjectionType projType=(ProjectionType)1000) const;
 
@@ -210,31 +213,35 @@
 
 	//! Transform from heliocentric coordinate to equatorial at current equinox (for the planet where the observer stands)
 	Vec3d heliocentricEclipticToEquinoxEqu(const Vec3d& v) const;
-	//! Transform vector from heliocentric coordinate to false equatorial : equatorial
-	//! coordinate but centered on the observer position (usefull for objects close to earth)
-	Vec3d heliocentricEclipticToEarthPosEquinoxEqu(const Vec3d& v) const;
+//	//! Transform vector from heliocentric coordinate to false equatorial : equatorial
+//	//! coordinate but centered on the observer position (useful for objects close to earth)
+//	//! Unused as of V0.13
+//	Vec3d heliocentricEclipticToEarthPosEquinoxEqu(const Vec3d& v) const;
 
-	//! Get the modelview matrix for heliocentric ecliptic (Vsop87) drawing
+	//! Get the modelview matrix for heliocentric ecliptic (Vsop87) drawing.
 	StelProjector::ModelViewTranformP getHeliocentricEclipticModelViewTransform(RefractionMode refMode=RefractionAuto) const;
 
-	//! Get the modelview matrix for observer-centric ecliptic (Vsop87) drawing
-	StelProjector::ModelViewTranformP getObservercentricEclipticModelViewTransform(RefractionMode refMode=RefractionAuto) const;
-
-	//! Get the modelview matrix for observer-centric equatorial at equinox drawing
+	//! Get the modelview matrix for observer-centric ecliptic (Vsop87) drawing.
+	StelProjector::ModelViewTranformP getObservercentricEclipticJ2000ModelViewTransform(RefractionMode refMode=RefractionAuto) const;
+
+	//! Get the modelview matrix for observer-centric ecliptic of Date drawing.
+	StelProjector::ModelViewTranformP getObservercentricEclipticOfDateModelViewTransform(RefractionMode refMode=RefractionAuto) const;
+
+	//! Get the modelview matrix for observer-centric equatorial at equinox drawing.
 	StelProjector::ModelViewTranformP getEquinoxEquModelViewTransform(RefractionMode refMode=RefractionAuto) const;
 
-	//! Get the modelview matrix for observer-centric altazimuthal drawing
+	//! Get the modelview matrix for observer-centric altazimuthal drawing.
 	StelProjector::ModelViewTranformP getAltAzModelViewTransform(RefractionMode refMode=RefractionAuto) const;
 
-	//! Get the modelview matrix for observer-centric J2000 equatorial drawing
+	//! Get the modelview matrix for observer-centric J2000 equatorial drawing.
 	StelProjector::ModelViewTranformP getJ2000ModelViewTransform(RefractionMode refMode=RefractionAuto) const;
 
-	//! Get the modelview matrix for observer-centric Galactic equatorial drawing
+	//! Get the modelview matrix for observer-centric Galactic equatorial drawing.
 	StelProjector::ModelViewTranformP getGalacticModelViewTransform(RefractionMode refMode=RefractionAuto) const;
 
-	//! Rotation matrix from equatorial J2000 to ecliptic (Vsop87)
+	//! Rotation matrix from equatorial J2000 to ecliptic (VSOP87A).
 	static const Mat4d matJ2000ToVsop87;
-	//! Rotation matrix from ecliptic (Vsop87) to equatorial J2000
+	//! Rotation matrix from ecliptic (VSOP87A) to equatorial J2000.
 	static const Mat4d matVsop87ToJ2000;
 	//! Rotation matrix from J2000 to Galactic reference frame, using FITS convention.
 	static const Mat4d matJ2000ToGalactic;
@@ -249,6 +256,10 @@
 
 	const QSharedPointer<class Planet> getCurrentPlanet() const;
 
+	//! Unfortunately we also need this.
+	const StelObserver* getCurrentObserver() const;
+
+
 	SphericalCap getVisibleSkyArea() const;
 	
 	//! Smoothly move the observer to the given location
@@ -291,10 +302,12 @@
 	//! @return valid range
 	QString getCurrentDeltaTAlgorithmValidRange(double jDay, QString* marker) const;
 
-	//! Checks for current time of day - it's night or day?
+	//! Checks for altitude of sun - is it night or day?
+	//! @return true if sun higher than about -6 degrees, i.e. "day" includes civil twilight.
+	//! @note Useful mostly for brightness-controlled GUI decisions like font colors.
 	bool isDay() const;
 
-	//! Get value of the current Julian epoch
+	//! Get value of the current Julian epoch (i.e. current year with decimal fraction, e.g. 2012.34567)
 	double getCurrentEpoch() const;
 
 	//! Get the default Mapping used by the Projection
@@ -451,6 +464,10 @@
 	void addTropicalMonth();
 	//! Add one mean tropical year to the simulation time.
 	void addTropicalYear();
+	//! Add one mean tropical century to the simulation time.
+	void addTropicalCentury();
+	//! Add one Julian century to the simulation time.
+	void addJulianCentury();
 
 	//! Subtract one synodic month to the simulation time.
 	void subtractSynodicMonth();
@@ -466,7 +483,11 @@
 	//! Subtract one mean tropical month to the simulation time.
 	void subtractTropicalMonth();
 	//! Subtract one mean tropical year to the simulation time.
-	void subtractTropicalYear();	
+	void subtractTropicalYear();
+	//! Subtract one mean tropical century to the simulation time.
+	void subtractTropicalCentury();
+	//! Subtract one Julian century to the simulation time.
+	void subtractJulianCentury();
 
 	//! Add a number of Earth Solar days to the current simulation time
 	//! @param d the decimal number of days to add (use negative values to subtract)
@@ -525,13 +546,17 @@
 	void resetSync();
 
 	// Matrices used for every coordinate transfo
-	Mat4d matHeliocentricEclipticToAltAz;      // Transform from heliocentric ecliptic (Vsop87) to observer-centric altazimuthal coordinate
-	Mat4d matAltAzToHeliocentricEcliptic;	   // Transform from observer-centric altazimuthal coordinate to heliocentric ecliptic (Vsop87)
-	Mat4d matAltAzToEquinoxEqu;                // Transform from observer-centric altazimuthal coordinate to Earth Equatorial
-	Mat4d matEquinoxEquToAltAz;                // Transform from observer-centric altazimuthal coordinate to Earth Equatorial
-	Mat4d matHeliocentricEclipticToEquinoxEqu; // Transform from heliocentric ecliptic (Vsop87) to earth equatorial coordinate
-	Mat4d matEquinoxEquToJ2000;
-	Mat4d matJ2000ToEquinoxEqu;
+	Mat4d matHeliocentricEclipticJ2000ToAltAz; // Transform from heliocentric ecliptic Cartesian (VSOP87A) to topocentric (StelObserver) altazimuthal coordinate
+	Mat4d matAltAzToHeliocentricEclipticJ2000; // Transform from topocentric (StelObserver) altazimuthal coordinate to heliocentric ecliptic Cartesian (VSOP87A)
+	Mat4d matAltAzToEquinoxEqu;                // Transform from topocentric altazimuthal coordinate to Earth Equatorial
+	Mat4d matEquinoxEquToAltAz;                // Transform from Earth Equatorial to topocentric (StelObserver) altazimuthal coordinate
+	Mat4d matHeliocentricEclipticToEquinoxEqu; // Transform from heliocentric ecliptic Cartesian (VSOP87A) to earth equatorial coordinate
+	Mat4d matEquinoxEquToJ2000;                // GZ For Earth, this should be inverse precession matrix. Yes, =Rz(VSOPoffset)Rx(eps0)Rz(-psiA)Rx(-omA)Rz(chiA)
+	Mat4d matJ2000ToEquinoxEqu;                // GZ: Should be precession matrix?
+//	Mat4d matEclOfDateToVsop87;                // GZ NEW: precession of the ecliptic
+//	Mat4d matVsop87ToEclOfDate;                // GZ NEW: precession of the ecliptic
+
+
 	Mat4d matJ2000ToAltAz;
 
 	Mat4d matAltAzModelView;           // Modelview matrix for observer-centric altazimuthal drawing

=== modified file 'src/core/StelObject.cpp'
--- src/core/StelObject.cpp	2015-06-12 18:45:39 +0000
+++ src/core/StelObject.cpp	2015-07-28 19:18:20 +0000
@@ -28,6 +28,7 @@
 #include "RefractionExtinction.hpp"
 #include "StelLocation.hpp"
 #include "SolarSystem.hpp"
+#include "StelModuleMgr.hpp"
 
 #include <QRegExp>
 #include <QDebug>
@@ -42,6 +43,7 @@
 Vec3d StelObject::getSiderealPosGeometric(const StelCore* core) const
 {
 	// Hour Angle corrected to Delta-T value
+	// TODO: make code readable by calling siderealTime(JD_UT), this should not contain a deltaT in its algorithm.
 	double dt = (core->getDeltaT(core->getJDay())/240.)*M_PI/180.;
 	return Mat4d::zrotation(-core->getLocalSiderealTime()+dt)* getEquinoxEquatorialPos(core);
 }
@@ -52,6 +54,7 @@
 	Vec3d v=getAltAzPosApparent(core);
 	v = core->altAzToEquinoxEqu(v, StelCore::RefractionOff);
 	// Hour Angle corrected to Delta-T value
+	// TODO: make code readable by calling siderealTime(JD_UT), this should not contain a deltaT in its algorithm.
 	double dt = (core->getDeltaT(core->getJDay())/240.)*M_PI/180.;
 	return Mat4d::zrotation(-core->getLocalSiderealTime()+dt)*v;
 }
@@ -109,6 +112,9 @@
 {
 	bool withAtmosphere = core->getSkyDrawer()->getFlagHasAtmosphere();
 	bool withDecimalDegree = StelApp::getInstance().getFlagShowDecimalDegrees();;
+	double az_app, alt_app;
+	StelUtils::rectToSphe(&az_app,&alt_app,getAltAzPosApparent(core));
+	Q_UNUSED(az_app);
 	QString cepoch = qc_("on date", "coordinates for current epoch");
 	QString res;
 	if (flags&RaDecJ2000)
@@ -137,7 +143,7 @@
 		QString hadec;
 		StelUtils::rectToSphe(&ra_sidereal,&dec_sidereal,getSiderealPosGeometric(core));
 		ra_sidereal = 2.*M_PI-ra_sidereal;
-		if (withAtmosphere)
+		if (withAtmosphere && (alt_app>-3.0*M_PI/180.0)) // Don't show refracted values much below horizon where model is meaningless.
 		{
 			StelUtils::rectToSphe(&ra_sidereal,&dec_sidereal,getSiderealPosApparent(core));
 			ra_sidereal = 2.*M_PI-ra_sidereal;
@@ -175,16 +181,12 @@
 		az = 3.*M_PI - az;  // N is zero, E is 90 degrees
 		if (az > M_PI*2)
 			az -= M_PI*2;
-		if (withAtmosphere)
+		if (withAtmosphere && (alt_app>-3.0*M_PI/180.0)) // Don't show refracted altitude much below horizon where model is meaningless.
 		{
-			StelUtils::rectToSphe(&az,&alt,getAltAzPosApparent(core));
-			az = 3.*M_PI - az;  // N is zero, E is 90 degrees
-			if (az > M_PI*2)
-				az -= M_PI*2;
 			if (withDecimalDegree)
-				res += q_("Az/Alt: %1/%2").arg(StelUtils::radToDecDegStr(az), StelUtils::radToDecDegStr(alt)) + " " + q_("(apparent)") + "<br>";
+				res += q_("Az/Alt: %1/%2").arg(StelUtils::radToDecDegStr(az), StelUtils::radToDecDegStr(alt_app)) + " " + q_("(apparent)") + "<br>";
 			else
-				res += q_("Az/Alt: %1/%2").arg(StelUtils::radToDmsStr(az,true), StelUtils::radToDmsStr(alt,true)) + " " + q_("(apparent)") + "<br>";
+				res += q_("Az/Alt: %1/%2").arg(StelUtils::radToDmsStr(az,true), StelUtils::radToDmsStr(alt_app,true)) + " " + q_("(apparent)") + "<br>";
 		}
 		else
 		{
@@ -197,7 +199,15 @@
 
 	if (flags&EclipticCoord)
 	{
-		double ecl = core->getCurrentPlanet()->getRotObliquity(2451545.0);
+		// N.B. Ecliptical coordinates are particularly earth-bound.
+		// It may be OK to have terrestrial ecliptical coordinates of J2000.0 (standard epoch) because those are in practice linked with VSOP XY plane,
+		// and because the ecliptical grid of J2000 is also shown for observers on other planets.
+		// The formulation here has never computed the true position of any observer planet's orbital plane except for Earth,
+		// or ever displayed the coordinates in the observer planet's equivalent to Earth's ecliptical coordinates.
+		// As quick test you can observe if in any "Ecliptic coordinate" as seen from e.g. Mars or Jupiter the Sun was ever close to beta=0.
+
+		//double ecl = core->getCurrentPlanet()->getRotObliquity(2451545.0);
+		double ecl=GETSTELMODULE(SolarSystem)->getEarth()->getRotObliquity(2451545.0);
 		double ra_equ, dec_equ, lambda, beta;
 		StelUtils::rectToSphe(&ra_equ,&dec_equ,getJ2000EquatorialPos(core));
 		StelUtils::equToEcl(ra_equ, dec_equ, ecl, &lambda, &beta);
@@ -206,14 +216,24 @@
 			res += q_("Ecliptic longitude/latitude") + QString(" (J%1): %2/%3").arg(QString::number(2000.f, 'f', 1), StelUtils::radToDecDegStr(lambda), StelUtils::radToDecDegStr(beta)) + "<br>";
 		else
 			res += q_("Ecliptic longitude/latitude") + QString(" (J%1): %2/%3").arg(QString::number(2000.f, 'f', 1), StelUtils::radToDmsStr(lambda, true), StelUtils::radToDmsStr(beta, true)) + "<br>";
-		ecl = core->getCurrentPlanet()->getRotObliquity(core->getJDay());
-		StelUtils::rectToSphe(&ra_equ,&dec_equ,getEquinoxEquatorialPos(core));
-		StelUtils::equToEcl(ra_equ, dec_equ, ecl, &lambda, &beta);
-		if (lambda<0) lambda+=2.0*M_PI;
-		if (withDecimalDegree)
-			res += q_("Ecliptic longitude/latitude") + QString(" (%1): %2/%3").arg(cepoch, StelUtils::radToDecDegStr(lambda), StelUtils::radToDecDegStr(beta)) + "<br>";
-		else
-			res += q_("Ecliptic longitude/latitude") + QString(" (%1): %2/%3").arg(cepoch, StelUtils::radToDmsStr(lambda, true), StelUtils::radToDmsStr(beta, true)) + "<br>";
+
+		if (core->getCurrentPlanet()->getEnglishName()=="Earth")
+		{
+			ecl = GETSTELMODULE(SolarSystem)->getEarth()->getRotObliquity(2451545.0);
+
+			StelUtils::rectToSphe(&ra_equ,&dec_equ,getEquinoxEquatorialPos(core));
+			StelUtils::equToEcl(ra_equ, dec_equ, ecl, &lambda, &beta);
+			if (lambda<0) lambda+=2.0*M_PI;
+			if (withDecimalDegree)
+				res += q_("Ecliptic longitude/latitude") + QString(" (%1): %2/%3").arg(cepoch, StelUtils::radToDecDegStr(lambda), StelUtils::radToDecDegStr(beta)) + "<br>";
+			else
+				res += q_("Ecliptic longitude/latitude") + QString(" (%1): %2/%3").arg(cepoch, StelUtils::radToDmsStr(lambda, true), StelUtils::radToDmsStr(beta, true)) + "<br>";
+			// GZ Only for now: display epsilon_A, angle between Earth's Axis and ecl. of date.
+			if (withDecimalDegree)
+				res += q_("Ecliptic obliquity") + QString(" (%1): %2").arg(cepoch, StelUtils::radToDecDegStr(ecl)) + "<br>";
+			else
+				res += q_("Ecliptic obliquity") + QString(" (%1): %2").arg(cepoch, StelUtils::radToDmsStr(ecl)) + "<br>";
+		}
 	}
 
 	if (flags&GalacticCoord)
@@ -249,8 +269,8 @@
 		StelCore* core = StelApp::getInstance().getCore();
 		if (core->isDay() && core->getSkyDrawer()->getFlagHasAtmosphere()==true)
 		{
-			// Let's make info text is more readable when atmosphere enabled at daylight.
-			color = StelUtils::strToVec3f(StelApp::getInstance().getSettings()->value("color/daylight_color", "0.0,0.0,0.0").toString());
+			// make info text more readable when atmosphere enabled at daylight.
+			color = StelUtils::strToVec3f(StelApp::getInstance().getSettings()->value("color/daylight_text_color", "0.0,0.0,0.0").toString());
 		}
 		str.prepend(QString("<font color=%1>").arg(StelUtils::vec3fToHtmlColor(color)));
 		str.append(QString("</font>"));

=== modified file 'src/core/StelObject.hpp'
--- src/core/StelObject.hpp	2014-10-17 22:54:15 +0000
+++ src/core/StelObject.hpp	2015-07-28 19:18:20 +0000
@@ -57,13 +57,23 @@
 		GalacticCoord		= 0x00000800, //!< The galactic position
 		ObjectType		= 0x00001000, //!< The type of the object (star, planet, etc.)
 		EclipticCoord		= 0x00002000, //!< The ecliptic position
-		PlainText		= 0x00004000  //!< Strip HTML tags from output
+		EclipticCoordXYZ	= 0x00004000, //!< The ecliptic position, XYZ of VSOP87A (used mainly for debugging, not public)
+		PlainText		= 0x00010000,  //!< Strip HTML tags from output
+// TODO GZ
+//		RaDecJ2000Planetocentric  = 0x00020000, //!< The planetocentric equatorial position (J2000 ref) [Mostly to compare with almanacs]
+//		RaDecOfDatePlanetocentric = 0x00040000  //!< The planetocentric equatorial position (of date)
+//		// and split Ecliptical into
+//		EclipticCoordJ2000	= 0x00002000, //!< The ecliptic position w.r.t. ecliptic of eq.J2000.0
+//		EclipticCoordOfDate	= 0x00002000, //!< The ecliptic position w.r.t. ecliptic of eq. of date
+
+
 	};
 	typedef QFlags<InfoStringGroupFlags> InfoStringGroup;
 	Q_FLAGS(InfoStringGroup)
 
 	//! A pre-defined set of specifiers for the getInfoString flags argument to getInfoString
-	static const InfoStringGroupFlags AllInfo = (InfoStringGroupFlags)(Name|CatalogNumber|Magnitude|RaDecJ2000|RaDecOfDate|AltAzi|Distance|Size|Extra|HourAngle|AbsoluteMagnitude|GalacticCoord|ObjectType|EclipticCoord);
+	static const InfoStringGroupFlags AllInfo = (InfoStringGroupFlags)(Name|CatalogNumber|Magnitude|RaDecJ2000|RaDecOfDate|AltAzi|Distance|Size|Extra|HourAngle|
+									   AbsoluteMagnitude|GalacticCoord|ObjectType|EclipticCoord|EclipticCoordXYZ);
 	//! A pre-defined set of specifiers for the getInfoString flags argument to getInfoString
 	static const InfoStringGroupFlags ShortInfo = (InfoStringGroupFlags)(Name|CatalogNumber|Magnitude|RaDecJ2000);
 

=== modified file 'src/core/StelObserver.cpp'
--- src/core/StelObserver.cpp	2015-02-01 20:44:54 +0000
+++ src/core/StelObserver.cpp	2015-07-28 19:18:20 +0000
@@ -183,6 +183,7 @@
 
 const QSharedPointer<Planet> StelObserver::getHomePlanet(void) const
 {
+	Q_ASSERT(planet);
 	return planet;
 }
 
@@ -191,22 +192,47 @@
 	return getHomePlanet()->getHeliocentricEclipticPos();
 }
 
+// Used to approximate solution with assuming a spherical planet.
+// Since V0.14, following Meeus, Astr. Alg. 2nd ed, Ch.11.
 double StelObserver::getDistanceFromCenter(void) const
 {
-	return getHomePlanet()->getRadius() + (currentLocation.altitude/(1000*AU));
+	if (getHomePlanet()->getRadius()==0.0) // the transitional ArtificialPlanet od SpaceShipObserver has this
+		return currentLocation.altitude/(1000*AU);
+
+	double a=getHomePlanet()->getRadius();
+	double bByA = getHomePlanet()->getOneMinusOblateness(); // b/a;
+
+	if (fabs(currentLocation.latitude)>=89.9) // avoid tan(90) issues.
+		return a * bByA;
+
+	double latRad=currentLocation.latitude*(M_PI/180.0);
+	double u = atan( bByA * tan(latRad));
+	// qDebug() << "getDistanceFromCenter: a=" << a*AU << "b/a=" << bByA << "b=" << bByA*a *AU  << "latRad=" << latRad << "u=" << u;
+	Q_ASSERT(fabs(u)<= fabs(latRad));
+	double altFix=(currentLocation.altitude/(1000.0*AU)) / a;
+
+	double rhoSinPhiPrime= bByA * sin(u) + altFix*sin(latRad);
+	double rhoCosPhiPrime= cos(u) + altFix*cos(latRad);
+
+	double rho = sqrt(rhoSinPhiPrime*rhoSinPhiPrime+rhoCosPhiPrime*rhoCosPhiPrime);
+	return rho*a;
 }
 
 Mat4d StelObserver::getRotAltAzToEquatorial(double jd) const
 {
 	double lat = currentLocation.latitude;
-	// TODO: Figure out how to keep continuity in sky as reach poles
+	// TODO: Figure out how to keep continuity in sky as we reach poles
 	// otherwise sky jumps in rotation when reach poles in equatorial mode
 	// This is a kludge
+	// GZ: Actually, why would that be? Lat should be clamped elsewhere. Added tests.
+	Q_ASSERT(lat <=  90.0);
+	Q_ASSERT(lat >= -90.0);
 	if( lat > 90.0 )  lat = 90.0;
 	if( lat < -90.0 ) lat = -90.0;
 	// Include a DeltaT correction. Sidereal time and longitude here are both in degrees, but DeltaT in seconds of time.
 	// 360 degrees = 24hrs; 15 degrees = 1hr = 3600s; 1 degree = 240s
 	// Apply DeltaT correction only for Earth
+	// TODO: make code readable by calling siderealTime(JD_UT), this should not contain a deltaT in its algorithm.
 	double deltaT = 0.;
 	if (getHomePlanet()->getEnglishName()=="Earth")
 		deltaT = StelApp::getInstance().getCore()->getDeltaT(jd)/240.;

=== modified file 'src/core/VecMath.hpp'
--- src/core/VecMath.hpp	2015-04-01 14:36:44 +0000
+++ src/core/VecMath.hpp	2015-07-28 19:18:20 +0000
@@ -241,6 +241,7 @@
 	inline void normalize();
 
 	inline void transfo4d(const Mat4d&);
+	QString toString() const {return QString("[%1, %2, %3, %4]").arg(v[0]).arg(v[1]).arg(v[2]).arg(v[3]);}
 
 	T v[4];		// The 4 values
 };
@@ -273,8 +274,22 @@
 
 	Matrix3<T> transpose() const;
 	Matrix3<T> inverse() const;
+	//! return trace (sum of diagonal elements).
+	inline T trace() const {return r[0]+r[4]+r[8];}
+	//! return rotational angle
+	inline T angle() const {return acos(0.5*(this->trace()-1.0));}
 
 	inline void print(void) const;
+	QString toString(int fieldWidth=0, char format='g', int precision=-1) const {return QString("[[%1, %2, %3], [%4, %5, %6], [%7, %8, %9]]")
+				.arg(r[0], fieldWidth, format, precision)
+				.arg(r[1], fieldWidth, format, precision)
+				.arg(r[2], fieldWidth, format, precision)
+				.arg(r[3], fieldWidth, format, precision)
+				.arg(r[4], fieldWidth, format, precision)
+				.arg(r[5], fieldWidth, format, precision)
+				.arg(r[6], fieldWidth, format, precision)
+				.arg(r[7], fieldWidth, format, precision)
+				.arg(r[8], fieldWidth, format, precision);}
 
 	T r[9];
 };
@@ -322,8 +337,9 @@
 	Matrix4<T> transpose() const;
 	Matrix4<T> inverse() const;
 
-    //Returns the upper 3x3 Matrix of the current 4x4 Matrix
-    Matrix3<T> upper3x3() const;
+	//Returns the upper 3x3 Matrix of the current 4x4 Matrix
+	Matrix3<T> upper3x3() const;
+	Matrix3<T> upper3x3Transposed() const;
 
 	inline Vector4<T> getRow(const int row) const;
 	inline Vector4<T> getColumn(const int column) const;
@@ -332,6 +348,23 @@
 	inline QMatrix4x4 convertToQMatrix() const;
 
 	inline void print(void) const;
+	QString toString(int fieldWidth=0, char format='g', int precision=-1) const {return QString("[[%1, %2, %3, %4], [%5, %6, %7, %8], [%9, %10, %11, %12], [%13, %14, %15, %16]]")
+				.arg(r[0], fieldWidth, format, precision)
+				.arg(r[1], fieldWidth, format, precision)
+				.arg(r[2], fieldWidth, format, precision)
+				.arg(r[3], fieldWidth, format, precision)
+				.arg(r[4], fieldWidth, format, precision)
+				.arg(r[5], fieldWidth, format, precision)
+				.arg(r[6], fieldWidth, format, precision)
+				.arg(r[7], fieldWidth, format, precision)
+				.arg(r[8], fieldWidth, format, precision)
+				.arg(r[9], fieldWidth, format, precision)
+				.arg(r[10], fieldWidth, format, precision)
+				.arg(r[11], fieldWidth, format, precision)
+				.arg(r[12], fieldWidth, format, precision)
+				.arg(r[13], fieldWidth, format, precision)
+				.arg(r[14], fieldWidth, format, precision)
+				.arg(r[15], fieldWidth, format, precision);}
 
 	T r[16];
 };
@@ -1467,8 +1500,15 @@
 	#undef SWAP_ROWS
 }
 
+
 template<class T> Matrix3<T> Matrix4<T>::upper3x3() const
 {
+    return Matrix3<T>(r[0], r[1], r[2],
+		      r[4], r[5], r[6],
+		      r[8], r[9], r[10]);
+}
+template<class T> Matrix3<T> Matrix4<T>::upper3x3Transposed() const
+{
     return Matrix3<T>(r[0], r[4], r[8],
                       r[1], r[5], r[9],
                       r[2], r[6], r[10]);

=== modified file 'src/core/modules/GridLinesMgr.cpp'
--- src/core/modules/GridLinesMgr.cpp	2015-03-26 15:44:34 +0000
+++ src/core/modules/GridLinesMgr.cpp	2015-07-28 19:18:20 +0000
@@ -29,6 +29,7 @@
 #include "StelCore.hpp"
 #include "StelPainter.hpp"
 #include "StelSkyDrawer.hpp"
+#include "precession.h"
 
 #include <set>
 #include <QSettings>
@@ -66,15 +67,19 @@
 public:
 	enum SKY_LINE_TYPE
 	{
-		EQUATOR,
-		ECLIPTIC,
+		EQUATOR_J2000,
+		EQUATOR_OF_DATE,
+		ECLIPTIC_J2000,
+		ECLIPTIC_OF_DATE,
+		PRECESSIONCIRCLE_N,
+		PRECESSIONCIRCLE_S,
 		MERIDIAN,
 		HORIZON,
 		GALACTICEQUATOR,
 		LONGITUDE
 	};
 	// Create and precompute positions of a SkyGrid
-	SkyLine(SKY_LINE_TYPE _line_type = EQUATOR);
+	SkyLine(SKY_LINE_TYPE _line_type = EQUATOR_J2000);
 	virtual ~SkyLine();
 	void draw(StelCore* core) const;
 	void setColor(const Vec3f& c) {color = c;}
@@ -202,7 +207,8 @@
 
 				break;			
 			}
-			case StelCore::FrameObservercentricEcliptic:						
+			case StelCore::FrameObservercentricEclipticJ2000:
+			case StelCore::FrameObservercentricEclipticOfDate:
 			{
 				double raAngle = d->raAngle;
 				if (raAngle<0.)
@@ -355,12 +361,11 @@
 	if (QOpenGLContext::currentContext()->format().renderableType()==QSurfaceFormat::OpenGL)
 		glEnable(GL_LINE_SMOOTH);
 	#endif
-	Vec4f textColor(color[0], color[1], color[2], 0);
+
+	// make text colors just a bit brighter. (But if >1, QColor::setRgb fails and makes text invisible.)
+	Vec4f textColor(qMin(1.0f, 1.25f*color[0]), qMin(1.0f, 1.25f*color[1]), qMin(1.0f, 1.25f*color[2]), fader.getInterstate());
 	sPainter.setColor(color[0],color[1],color[2], fader.getInterstate());
 
-	textColor*=2;
-	textColor[3]=fader.getInterstate();
-
 	sPainter.setFont(font);
 	ViewportEdgeIntersectCallbackData userData(&sPainter);
 	userData.textColor = textColor;
@@ -586,14 +591,27 @@
 			frameType = StelCore::FrameAltAz;
 			label = q_("Meridian");
 			break;
-		case ECLIPTIC:
-			frameType = StelCore::FrameObservercentricEcliptic;
-			label = q_("Ecliptic");
-			break;
-		case EQUATOR:
+		case ECLIPTIC_J2000:
+			frameType = StelCore::FrameObservercentricEclipticJ2000;
+			label = q_("Ecliptic of J2000.0");
+			break;
+		case ECLIPTIC_OF_DATE:
+			frameType = StelCore::FrameObservercentricEclipticOfDate;
+			label = q_("Ecliptic of Date");
+			break;
+		case EQUATOR_J2000:
+			frameType = StelCore::FrameJ2000;
+			label = q_("Equator of J2000.0");
+			break;
+		case EQUATOR_OF_DATE:
 			frameType = StelCore::FrameEquinoxEqu;
 			label = q_("Equator");
 			break;
+		case PRECESSIONCIRCLE_N:
+		case PRECESSIONCIRCLE_S:
+			frameType = StelCore::FrameObservercentricEclipticOfDate;
+			label = q_("Precession Circle");
+			break;
 		case HORIZON:
 			frameType = StelCore::FrameAltAz;
 			label = q_("Horizon");
@@ -603,10 +621,12 @@
 			label = q_("Galactic Equator");
 			break;
 		case LONGITUDE:
-			frameType = StelCore::FrameObservercentricEcliptic;
+			frameType = StelCore::FrameObservercentricEclipticJ2000; // TODO: Switch to FrameObservercentriEclipticOfDate
 			// TRANSLATORS: Full term is "opposition/conjunction longitude"
 			label = q_("O./C. longitude");
 			break;
+		default:
+			Q_ASSERT(0);
 	}
 }
 
@@ -625,7 +645,10 @@
 	sPainter.setColor(color[0], color[1], color[2], fader.getInterstate());
 	glEnable(GL_BLEND);
 	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // Normal transparency mode
-
+	#ifdef GL_LINE_SMOOTH
+	if (QOpenGLContext::currentContext()->format().renderableType()==QSurfaceFormat::OpenGL)
+		glEnable(GL_LINE_SMOOTH);
+	#endif
 	Vec4f textColor(color[0], color[1], color[2], 0);		
 	textColor[3]=fader.getInterstate();
 
@@ -635,6 +658,79 @@
 	userData.text = label;
 	/////////////////////////////////////////////////
 	// Draw the line
+
+	// Precession circles are Small Circles, all others are Great Circles.
+	if (line_type==PRECESSIONCIRCLE_N || line_type==PRECESSIONCIRCLE_S)
+	{
+		const double lat=(line_type==PRECESSIONCIRCLE_S ? -1.0 : 1.0) * (M_PI/2.0-getPrecessionAngleVondrakCurrentEpsilonA());
+		SphericalCap declinationCap(Vec3d(0,0,1), std::sin(lat));
+		const Vec3d rotCenter(0,0,declinationCap.d);
+
+		Vec3d p1, p2;
+		if (!SphericalCap::intersectionPoints(viewPortSphericalCap, declinationCap, p1, p2))
+		{
+			if ((viewPortSphericalCap.d<declinationCap.d && viewPortSphericalCap.contains(declinationCap.n))
+				|| (viewPortSphericalCap.d<-declinationCap.d && viewPortSphericalCap.contains(-declinationCap.n)))
+			{
+				// The line is fully included in the viewport, draw it in 3 sub-arcs to avoid length > 180.
+				Vec3d pt1;
+				Vec3d pt2;
+				Vec3d pt3;
+				const double lon1=0.0;
+				const double lon2=120.0*M_PI/180.0;
+				const double lon3=240.0*M_PI/180.0;
+				StelUtils::spheToRect(lon1, lat, pt1); pt1.normalize();
+				StelUtils::spheToRect(lon2, lat, pt2); pt2.normalize();
+				StelUtils::spheToRect(lon3, lat, pt3); pt3.normalize();
+
+				sPainter.drawSmallCircleArc(pt1, pt2, rotCenter, viewportEdgeIntersectCallback, &userData);
+				sPainter.drawSmallCircleArc(pt2, pt3, rotCenter, viewportEdgeIntersectCallback, &userData);
+				sPainter.drawSmallCircleArc(pt3, pt1, rotCenter, viewportEdgeIntersectCallback, &userData);
+				#ifdef GL_LINE_SMOOTH
+				if (QOpenGLContext::currentContext()->format().renderableType()==QSurfaceFormat::OpenGL)
+					glDisable(GL_LINE_SMOOTH);
+				#endif
+				glDisable(GL_BLEND);
+				return;
+			}
+			else
+			{
+				#ifdef GL_LINE_SMOOTH
+				if (QOpenGLContext::currentContext()->format().renderableType()==QSurfaceFormat::OpenGL)
+					glDisable(GL_LINE_SMOOTH);
+				#endif
+				glDisable(GL_BLEND);
+				return;
+			}
+		}
+		// Draw the arc in 2 sub-arcs to avoid lengths > 180 deg
+		Vec3d middlePoint = p1-rotCenter+p2-rotCenter;
+		middlePoint.normalize();
+		middlePoint*=(p1-rotCenter).length();
+		middlePoint+=rotCenter;
+		if (!viewPortSphericalCap.contains(middlePoint))
+		{
+			middlePoint-=rotCenter;
+			middlePoint*=-1.;
+			middlePoint+=rotCenter;
+		}
+
+		sPainter.drawSmallCircleArc(p1, middlePoint, rotCenter,viewportEdgeIntersectCallback, &userData);
+		sPainter.drawSmallCircleArc(p2, middlePoint, rotCenter, viewportEdgeIntersectCallback, &userData);
+
+		// OpenGL ES 2.0 doesn't have GL_LINE_SMOOTH
+		#ifdef GL_LINE_SMOOTH
+		if (QOpenGLContext::currentContext()->format().renderableType()==QSurfaceFormat::OpenGL)
+			glDisable(GL_LINE_SMOOTH);
+		#endif
+
+		glDisable(GL_BLEND);
+
+
+		return;
+	}
+
+	// All the other "lines" are Great Circles
 	SphericalCap meridianSphericalCap(Vec3d(0,0,1), 0);	
 	Vec3d fpt(1,0,0);
 	if (line_type==MERIDIAN)
@@ -683,6 +779,14 @@
 	sPainter.drawGreatCircleArc(p1, middlePoint, NULL, viewportEdgeIntersectCallback, &userData);
 	sPainter.drawGreatCircleArc(p2, middlePoint, NULL, viewportEdgeIntersectCallback, &userData);
 
+	// OpenGL ES 2.0 doesn't have GL_LINE_SMOOTH
+	#ifdef GL_LINE_SMOOTH
+	if (QOpenGLContext::currentContext()->format().renderableType()==QSurfaceFormat::OpenGL)
+		glDisable(GL_LINE_SMOOTH);
+	#endif
+
+	glDisable(GL_BLEND);
+
 // 	// Johannes: use a big radius as a dirty workaround for the bug that the
 // 	// ecliptic line is not drawn around the observer, but around the sun:
 // 	const Vec3d vv(1000000,0,0);
@@ -694,11 +798,16 @@
 	setObjectName("GridLinesMgr");
 	equGrid = new SkyGrid(StelCore::FrameEquinoxEqu);
 	equJ2000Grid = new SkyGrid(StelCore::FrameJ2000);
-	eclJ2000Grid = new SkyGrid(StelCore::FrameObservercentricEcliptic);
+	eclJ2000Grid = new SkyGrid(StelCore::FrameObservercentricEclipticJ2000);
+	eclGrid = new SkyGrid(StelCore::FrameObservercentricEclipticOfDate);
 	galacticGrid = new SkyGrid(StelCore::FrameGalactic);
 	aziGrid = new SkyGrid(StelCore::FrameAltAz);
-	equatorLine = new SkyLine(SkyLine::EQUATOR);
-	eclipticLine = new SkyLine(SkyLine::ECLIPTIC);
+	equatorLine = new SkyLine(SkyLine::EQUATOR_OF_DATE);
+	equatorJ2000Line = new SkyLine(SkyLine::EQUATOR_J2000);
+	eclipticJ2000Line = new SkyLine(SkyLine::ECLIPTIC_J2000); // previous eclipticLine
+	eclipticLine = new SkyLine(SkyLine::ECLIPTIC_OF_DATE); // GZ NEW
+	precessionCircleN = new SkyLine(SkyLine::PRECESSIONCIRCLE_N);
+	precessionCircleS = new SkyLine(SkyLine::PRECESSIONCIRCLE_S);
 	meridianLine = new SkyLine(SkyLine::MERIDIAN);
 	horizonLine = new SkyLine(SkyLine::HORIZON);
 	galacticEquatorLine = new SkyLine(SkyLine::GALACTICEQUATOR);
@@ -710,10 +819,15 @@
 	delete equGrid;
 	delete equJ2000Grid;
 	delete eclJ2000Grid;
+	delete eclGrid;
 	delete galacticGrid;
 	delete aziGrid;
 	delete equatorLine;
+	delete equatorJ2000Line;
 	delete eclipticLine;
+	delete eclipticJ2000Line;
+	delete precessionCircleN;
+	delete precessionCircleS;
 	delete meridianLine;
 	delete horizonLine;
 	delete galacticEquatorLine;
@@ -739,9 +853,13 @@
 	setFlagEquatorGrid(conf->value("viewing/flag_equatorial_grid").toBool());
 	setFlagEquatorJ2000Grid(conf->value("viewing/flag_equatorial_J2000_grid").toBool());
 	setFlagEclipticJ2000Grid(conf->value("viewing/flag_ecliptic_J2000_grid").toBool());
+	setFlagEclipticGrid(conf->value("viewing/flag_ecliptic_grid").toBool());
 	setFlagGalacticGrid(conf->value("viewing/flag_galactic_grid").toBool());
 	setFlagEquatorLine(conf->value("viewing/flag_equator_line").toBool());
+	setFlagEquatorJ2000Line(conf->value("viewing/flag_equator_J2000_line").toBool());
 	setFlagEclipticLine(conf->value("viewing/flag_ecliptic_line").toBool());
+	setFlagEclipticJ2000Line(conf->value("viewing/flag_ecliptic_J2000_line").toBool());
+	setFlagPrecessionCircles(conf->value("viewing/flag_precession_circles").toBool());
 	setFlagMeridianLine(conf->value("viewing/flag_meridian_line").toBool());
 	setFlagHorizonLine(conf->value("viewing/flag_horizon_line").toBool());
 	setFlagGalacticEquatorLine(conf->value("viewing/flag_galactic_equator_line").toBool());
@@ -755,14 +873,18 @@
 	addAction("actionShow_Equatorial_Grid", displayGroup, N_("Equatorial grid"), "equatorGridDisplayed", "E");
 	addAction("actionShow_Azimuthal_Grid", displayGroup, N_("Azimuthal grid"), "azimuthalGridDisplayed", "Z");
 	addAction("actionShow_Ecliptic_Line", displayGroup, N_("Ecliptic line"), "eclipticLineDisplayed", ",");
+	addAction("actionShow_Ecliptic_J2000_Line", displayGroup, N_("Ecliptic J2000 line"), "eclipticJ2000LineDisplayed");
 	addAction("actionShow_Equator_Line", displayGroup, N_("Equator line"), "equatorLineDisplayed", ".");
+	addAction("actionShow_Equator_J2000_Line", displayGroup, N_("Equator J2000 line"), "equatorJ2000LineDisplayed"); // or with Hotkey??
 	addAction("actionShow_Meridian_Line", displayGroup, N_("Meridian line"), "meridianLineDisplayed", ";");
 	addAction("actionShow_Horizon_Line", displayGroup, N_("Horizon line"), "horizonLineDisplayed", "H");
 	addAction("actionShow_Equatorial_J2000_Grid", displayGroup, N_("Equatorial J2000 grid"), "equatorJ2000GridDisplayed");
 	addAction("actionShow_Ecliptic_J2000_Grid", displayGroup, N_("Ecliptic J2000 grid"), "eclipticJ2000GridDisplayed");
+	addAction("actionShow_Ecliptic_Grid", displayGroup, N_("Ecliptic grid"), "eclipticGridDisplayed");
 	addAction("actionShow_Galactic_Grid", displayGroup, N_("Galactic grid"), "galacticGridDisplayed");
 	addAction("actionShow_Galactic_Equator_Line", displayGroup, N_("Galactic equator"), "galacticEquatorLineDisplayed");
 	addAction("actionShow_Longitude_Line", displayGroup, N_("Opposition/conjunction longitude line"), "longitudeLineDisplayed");
+	addAction("actionShow_Precession_Circles", displayGroup, N_("Precession Circles"), "precessionCirclesDisplayed");
 }
 
 void GridLinesMgr::update(double deltaTime)
@@ -771,10 +893,15 @@
 	equGrid->update(deltaTime);
 	equJ2000Grid->update(deltaTime);
 	eclJ2000Grid->update(deltaTime);
+	eclGrid->update(deltaTime);
 	galacticGrid->update(deltaTime);
 	aziGrid->update(deltaTime);
 	equatorLine->update(deltaTime);
+	equatorJ2000Line->update(deltaTime);
 	eclipticLine->update(deltaTime);
+	eclipticJ2000Line->update(deltaTime);
+	precessionCircleN->update(deltaTime);
+	precessionCircleS->update(deltaTime);
 	meridianLine->update(deltaTime);
 	horizonLine->update(deltaTime);
 	galacticEquatorLine->update(deltaTime);
@@ -783,17 +910,30 @@
 
 void GridLinesMgr::draw(StelCore* core)
 {
-	equGrid->draw(core);
 	galacticGrid->draw(core);
+	eclJ2000Grid->draw(core);
+	// While ecliptic of J2000 may be helpful to get a feeling of the Z=0 plane of VSOP87,
+	// ecliptic of date is related to Earth and does not make much sense for the other planets.
+	// Of course, orbital plane of respective planet would be better, but is not implemented.
+	if (core->getCurrentPlanet()->getEnglishName()=="Earth")
+		eclGrid->draw(core);
 	equJ2000Grid->draw(core);
-	eclJ2000Grid->draw(core);
+	equGrid->draw(core);
 	aziGrid->draw(core);
+	// Lines after grids, to be able to e.g. draw equators in different color!
+	galacticEquatorLine->draw(core);
+	eclipticJ2000Line->draw(core);
+	if (core->getCurrentPlanet()->getEnglishName()=="Earth")
+	{
+		eclipticLine->draw(core);
+		precessionCircleN->draw(core);
+		precessionCircleS->draw(core);
+	}
+	longitudeLine->draw(core);
+	equatorJ2000Line->draw(core);
 	equatorLine->draw(core);
-	eclipticLine->draw(core);
 	meridianLine->draw(core);
 	horizonLine->draw(core);
-	galacticEquatorLine->draw(core);
-	longitudeLine->draw(core);
 }
 
 void GridLinesMgr::setStelStyle(const QString& section)
@@ -804,11 +944,14 @@
 	QString defaultColor = conf->value(section+"/default_color").toString();
 	setColorEquatorGrid(StelUtils::strToVec3f(conf->value(section+"/equatorial_color", defaultColor).toString()));
 	setColorEquatorJ2000Grid(StelUtils::strToVec3f(conf->value(section+"/equatorial_J2000_color", defaultColor).toString()));
-	setColorEclipticJ2000Grid(StelUtils::strToVec3f(conf->value(section+"/ecliptic_J2000_color", defaultColor).toString()));
+	setColorEclipticJ2000Grid(StelUtils::strToVec3f(conf->value(section+"/ecliptical_J2000_color", defaultColor).toString()));
+	setColorEclipticGrid(StelUtils::strToVec3f(conf->value(section+"/ecliptical_color", defaultColor).toString()));
 	setColorGalacticGrid(StelUtils::strToVec3f(conf->value(section+"/galactic_color", defaultColor).toString()));
 	setColorAzimuthalGrid(StelUtils::strToVec3f(conf->value(section+"/azimuthal_color", defaultColor).toString()));
 	setColorEquatorLine(StelUtils::strToVec3f(conf->value(section+"/equator_color", defaultColor).toString()));
 	setColorEclipticLine(StelUtils::strToVec3f(conf->value(section+"/ecliptic_color", defaultColor).toString()));
+	setColorEclipticJ2000Line(StelUtils::strToVec3f(conf->value(section+"/ecliptic_J2000_color", defaultColor).toString()));
+	setColorPrecessionCircles(StelUtils::strToVec3f(conf->value(section+"/precession_circles_color", defaultColor).toString()));
 	setColorMeridianLine(StelUtils::strToVec3f(conf->value(section+"/meridian_color", defaultColor).toString()));
 	setColorHorizonLine(StelUtils::strToVec3f(conf->value(section+"/horizon_color", defaultColor).toString()));
 	setColorGalacticEquatorLine(StelUtils::strToVec3f(conf->value(section+"/galactic_equator_color", defaultColor).toString()));
@@ -817,8 +960,12 @@
 
 void GridLinesMgr::updateLineLabels()
 {
+	equatorJ2000Line->updateLabel();
 	equatorLine->updateLabel();
 	eclipticLine->updateLabel();
+	eclipticJ2000Line->updateLabel();
+	precessionCircleN->updateLabel();
+	precessionCircleS->updateLabel();
 	meridianLine->updateLabel();
 	horizonLine->updateLabel();
 	galacticEquatorLine->updateLabel();
@@ -925,6 +1072,31 @@
 	}
 }
 
+//! Set flag for displaying Ecliptic of Date Grid
+void GridLinesMgr::setFlagEclipticGrid(const bool displayed)
+{
+	if(displayed != eclGrid->isDisplayed()) {
+		eclGrid->setDisplayed(displayed);
+		emit eclipticGridDisplayedChanged(displayed);
+	}
+}
+//! Get flag for displaying Ecliptic of Date Grid
+bool GridLinesMgr::getFlagEclipticGrid(void) const
+{
+	return eclGrid->isDisplayed();
+}
+Vec3f GridLinesMgr::getColorEclipticGrid(void) const
+{
+	return eclGrid->getColor();
+}
+void GridLinesMgr::setColorEclipticGrid(const Vec3f& newColor)
+{
+	if(newColor != eclGrid->getColor()) {
+		eclGrid->setColor(newColor);
+		emit eclipticGridColorChanged(newColor);
+	}
+}
+
 //! Set flag for displaying Galactic Grid
 void GridLinesMgr::setFlagGalacticGrid(const bool displayed)
 {
@@ -975,6 +1147,31 @@
 	}
 }
 
+//! Set flag for displaying J2000 Equatorial Line
+void GridLinesMgr::setFlagEquatorJ2000Line(const bool displayed)
+{
+	if(displayed != equatorJ2000Line->isDisplayed()) {
+		equatorJ2000Line->setDisplayed(displayed);
+		emit equatorJ2000LineDisplayedChanged(displayed);
+	}
+}
+//! Get flag for displaying J2000 Equatorial Line
+bool GridLinesMgr::getFlagEquatorJ2000Line(void) const
+{
+	return equatorJ2000Line->isDisplayed();
+}
+Vec3f GridLinesMgr::getColorEquatorJ2000Line(void) const
+{
+	return equatorJ2000Line->getColor();
+}
+void GridLinesMgr::setColorEquatorJ2000Line(const Vec3f& newColor)
+{
+	if(newColor != equatorJ2000Line->getColor()) {
+		equatorJ2000Line->setColor(newColor);
+		emit equatorJ2000LineColorChanged(newColor);
+	}
+}
+
 //! Set flag for displaying Ecliptic Line
 void GridLinesMgr::setFlagEclipticLine(const bool displayed)
 {
@@ -1000,6 +1197,58 @@
 	}
 }
 
+//! Set flag for displaying Ecliptic J2000 Line
+void GridLinesMgr::setFlagEclipticJ2000Line(const bool displayed)
+{
+	if(displayed != eclipticJ2000Line->isDisplayed()) {
+		eclipticJ2000Line->setDisplayed(displayed);
+		emit eclipticJ2000LineDisplayedChanged(displayed);
+	}
+}
+//! Get flag for displaying Ecliptic J2000 Line
+bool GridLinesMgr::getFlagEclipticJ2000Line(void) const
+{
+	return eclipticJ2000Line->isDisplayed();
+}
+Vec3f GridLinesMgr::getColorEclipticJ2000Line(void) const
+{
+	return eclipticJ2000Line->getColor();
+}
+void GridLinesMgr::setColorEclipticJ2000Line(const Vec3f& newColor)
+{
+	if(newColor != eclipticJ2000Line->getColor()) {
+		eclipticJ2000Line->setColor(newColor);
+		emit eclipticJ2000LineColorChanged(newColor);
+	}
+}
+
+//! Set flag for displaying Precession Circles
+void GridLinesMgr::setFlagPrecessionCircles(const bool displayed)
+{
+	if(displayed != precessionCircleN->isDisplayed()) {
+		precessionCircleN->setDisplayed(displayed);
+		precessionCircleS->setDisplayed(displayed);
+		emit precessionCirclesDisplayedChanged(displayed);
+	}
+}
+//! Get flag for displaying Precession Circles
+bool GridLinesMgr::getFlagPrecessionCircles(void) const
+{
+	// precessionCircleS is always synchronous, no separate queries.
+	return precessionCircleN->isDisplayed();
+}
+Vec3f GridLinesMgr::getColorPrecessionCircles(void) const
+{
+	return precessionCircleN->getColor();
+}
+void GridLinesMgr::setColorPrecessionCircles(const Vec3f& newColor)
+{
+	if(newColor != precessionCircleN->getColor()) {
+		precessionCircleN->setColor(newColor);
+		precessionCircleS->setColor(newColor);
+		emit precessionCirclesColorChanged(newColor);
+	}
+}
 
 //! Set flag for displaying Meridian Line
 void GridLinesMgr::setFlagMeridianLine(const bool displayed)

=== modified file 'src/core/modules/GridLinesMgr.hpp'
--- src/core/modules/GridLinesMgr.hpp	2015-02-24 16:53:57 +0000
+++ src/core/modules/GridLinesMgr.hpp	2015-07-28 19:18:20 +0000
@@ -1,6 +1,7 @@
 /*
  * Stellarium
  * Copyright (C) 2007 Fabien Chereau
+ * Copyright (C) 2015 Georg Zotti (more grids to illustrate precession issues)
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -27,8 +28,9 @@
 class SkyLine;
 
 //! @class GridLinesMgr
-//! The GridLinesMgr controls the drawing of the Azimuthal and Equatorial Grids,
-//! as well as the great circles: Meridian Line, Ecliptic Line and Equator Line.
+//! The GridLinesMgr controls the drawing of the Azimuthal, Equatorial, Ecliptical and Galactic Grids,
+//! as well as the great circles: Meridian Line, Ecliptic Lines of J2000.0 and date, Equator Line (of J2000.0 and date),
+//! Precession Circles, and a special line marking conjunction or opposition in ecliptical longitude (of date).
 class GridLinesMgr : public StelModule
 {
 	Q_OBJECT
@@ -40,6 +42,7 @@
 			   READ getColorAzimuthalGrid
 			   WRITE setColorAzimuthalGrid
 			   NOTIFY azimuthalGridColorChanged)
+
 	Q_PROPERTY(bool equatorGridDisplayed
 			   READ getFlagEquatorGrid
 			   WRITE setFlagEquatorGrid
@@ -48,18 +51,34 @@
 			   READ getColorEquatorGrid
 			   WRITE setColorEquatorGrid
 			   NOTIFY equatorGridColorChanged)
+
 	Q_PROPERTY(bool equatorJ2000GridDisplayed
 			   READ getFlagEquatorJ2000Grid
 			   WRITE setFlagEquatorJ2000Grid
 			   NOTIFY equatorJ2000GridDisplayedChanged)
+	Q_PROPERTY(Vec3f equatorJ2000GridColor
+			   READ getColorEquatorJ2000Grid
+			   WRITE setColorEquatorJ2000Grid
+			   NOTIFY equatorJ2000GridColorChanged)
+
 	Q_PROPERTY(bool eclipticJ2000GridDisplayed
 			   READ getFlagEclipticJ2000Grid
 			   WRITE setFlagEclipticJ2000Grid
 			   NOTIFY eclipticJ2000GridDisplayedChanged)
-	Q_PROPERTY(Vec3f equatorJ2000GridColor
-			   READ getColorEquatorJ2000Grid
-			   WRITE setColorEquatorJ2000Grid
-			   NOTIFY equatorJ2000GridColorChanged)
+	Q_PROPERTY(Vec3f eclipticJ2000GridColor
+			   READ getColorEclipticJ2000Grid
+			   WRITE setColorEclipticJ2000Grid
+			   NOTIFY eclipticJ2000GridColorChanged)
+	// NEW
+	Q_PROPERTY(bool eclipticGridDisplayed
+			   READ getFlagEclipticGrid
+			   WRITE setFlagEclipticGrid
+			   NOTIFY eclipticGridDisplayedChanged)
+	Q_PROPERTY(Vec3f eclipticGridColor
+			   READ getColorEclipticGrid
+			   WRITE setColorEclipticGrid
+			   NOTIFY eclipticGridColorChanged)
+
 	Q_PROPERTY(bool galacticGridDisplayed
 			   READ getFlagGalacticGrid
 			   WRITE setFlagGalacticGrid
@@ -68,6 +87,7 @@
 			   READ getColorGalacticGrid
 			   WRITE setColorGalacticGrid
 			   NOTIFY galacticGridColorChanged)
+
 	Q_PROPERTY(bool equatorLineDisplayed
 			   READ getFlagEquatorLine
 			   WRITE setFlagEquatorLine
@@ -76,6 +96,17 @@
 			   READ getColorEquatorLine
 			   WRITE setColorEquatorLine
 			   NOTIFY equatorLineColorChanged)
+
+	Q_PROPERTY(bool equatorJ2000LineDisplayed
+			   READ getFlagEquatorJ2000Line
+			   WRITE setFlagEquatorJ2000Line
+			   NOTIFY equatorJ2000LineDisplayedChanged)
+	Q_PROPERTY(Vec3f equatorJ2000LineColor
+			   READ getColorEquatorJ2000Line
+			   WRITE setColorEquatorJ2000Line
+			   NOTIFY equatorJ2000LineColorChanged)
+
+	// This is now ecl. of date.
 	Q_PROPERTY(bool eclipticLineDisplayed
 			   READ getFlagEclipticLine
 			   WRITE setFlagEclipticLine
@@ -84,6 +115,26 @@
 			   READ getColorEclipticLine
 			   WRITE setColorEclipticLine
 			   NOTIFY eclipticLineColorChanged)
+
+	// new name, but replaces old ecliptic.
+	Q_PROPERTY(bool eclipticJ2000LineDisplayed
+			   READ getFlagEclipticJ2000Line
+			   WRITE setFlagEclipticJ2000Line
+			   NOTIFY eclipticJ2000LineDisplayedChanged)
+	Q_PROPERTY(Vec3f eclipticJ2000LineColor
+			   READ getColorEclipticJ2000Line
+			   WRITE setColorEclipticJ2000Line
+			   NOTIFY eclipticJ2000LineColorChanged)
+
+	Q_PROPERTY(bool precessionCirclesDisplayed
+			   READ getFlagPrecessionCircles
+			   WRITE setFlagPrecessionCircles
+			   NOTIFY precessionCirclesDisplayedChanged)
+	Q_PROPERTY(Vec3f precessionCirclesColor
+			   READ getColorPrecessionCircles
+			   WRITE setColorPrecessionCircles
+			   NOTIFY precessionCirclesColorChanged)
+
 	Q_PROPERTY(bool meridianLineDisplayed
 			   READ getFlagMeridianLine
 			   WRITE setFlagMeridianLine
@@ -92,6 +143,7 @@
 			   READ getColorMeridianLine
 			   WRITE setColorMeridianLine
 			   NOTIFY meridianLineColorChanged)
+
 	Q_PROPERTY(bool longitudeLineDisplayed
 			   READ getFlagLongitudeLine
 			   WRITE setFlagLongitudeLine
@@ -100,6 +152,7 @@
 			   READ getColorLongitudeLine
 			   WRITE setColorLongitudeLine
 			   NOTIFY longitudeLineColorChanged)
+
 	Q_PROPERTY(bool horizonLineDisplayed
 			   READ getFlagHorizonLine
 			   WRITE setFlagHorizonLine
@@ -108,6 +161,7 @@
 			   READ getColorHorizonLine
 			   WRITE setColorHorizonLine
 			   NOTIFY horizonLineColorChanged)
+
 	Q_PROPERTY(bool galacticEquatorLineDisplayed
 			   READ getFlagGalacticEquatorLine
 			   WRITE setFlagGalacticEquatorLine
@@ -125,17 +179,17 @@
 	// Methods defined in the StelModule class
 	//! Initialize the GridLinesMgr. This process checks the values in the
 	//! application settings, and according to the settings there
-	//! sets the visibility of the Equatorial Grid, Azimuthal Grid, Meridian Line,
-	//! Equator Line and Ecliptic Line.
+	//! sets the visibility of the Equatorial Grids, Ecliptical Grids, Azimuthal Grid, Meridian Line,
+	//! Equator Line and Ecliptic Lines.
 	virtual void init();
 
-	//! Get the module ID, returns, "gridlines".
+	//! Get the module ID, returns "GridLinesMgr".
 	virtual QString getModuleID() const {return "GridLinesMgr";}
 
 	//! Draw the grids and great circle lines.
-	//! Draws the Equatorial Grid, Azimuthal Grid, Meridian Line, Equator Line
-	//! and Ecliptic Line according to the various flags which control their
-	//! visibility.
+	//! Draws the Equatorial Grids, Ecliptical Grids, Azimuthal Grid, Meridian Line, Equator Line,
+	//! Ecliptic Lines, Precession Circles, and Conjunction-Opposition Line according to the
+	//! various flags which control their visibility.
 	virtual void draw(StelCore* core);
 
 	//! Update time-dependent features.
@@ -176,9 +230,9 @@
 	//! @endcode
 	void setColorEquatorGrid(const Vec3f& newColor);
 
-	//! Setter for displaying Equatorial Grid.
+	//! Setter for displaying Equatorial J2000 Grid.
 	void setFlagEquatorJ2000Grid(const bool displayed);
-	//! Accessor for displaying Equatorial Grid.
+	//! Accessor for displaying Equatorial J2000 Grid.
 	bool getFlagEquatorJ2000Grid(void) const;
 	//! Get the current color of the Equatorial J2000 Grid.
 	Vec3f getColorEquatorJ2000Grid(void) const;
@@ -190,7 +244,7 @@
 	//! @endcode
 	void setColorEquatorJ2000Grid(const Vec3f& newColor);
 
-	//! Setter for displaying Ecliptic Grid.
+	//! Setter for displaying Ecliptic Grid of J2000.0.
 	void setFlagEclipticJ2000Grid(const bool displayed);
 	//! Accessor for displaying Ecliptic Grid.
 	bool getFlagEclipticJ2000Grid(void) const;
@@ -204,6 +258,20 @@
 	//! @endcode
 	void setColorEclipticJ2000Grid(const Vec3f& newColor);
 
+	//! Setter for displaying Ecliptic Grid of Date.
+	void setFlagEclipticGrid(const bool displayed);
+	//! Accessor for displaying Ecliptic Grid.
+	bool getFlagEclipticGrid(void) const;
+	//! Get the current color of the Ecliptic of Date Grid.
+	Vec3f getColorEclipticGrid(void) const;
+	//! Set the color of the Ecliptic Grid.
+	//! @param newColor The color of Ecliptic of Date grid
+	//! @code
+	//! // example of usage in scripts
+	//! GridLinesMgr.setColorEclipticGrid(Vec3f(1.0,0.0,0.0));
+	//! @endcode
+	void setColorEclipticGrid(const Vec3f& newColor);
+
 	//! Setter for displaying Galactic Grid.
 	void setFlagGalacticGrid(const bool displayed);
 	//! Accessor for displaying Galactic Grid.
@@ -232,6 +300,34 @@
 	//! @endcode
 	void setColorEquatorLine(const Vec3f& newColor);
 
+	//! Setter for displaying J2000 Equatorial Line.
+	void setFlagEquatorJ2000Line(const bool displayed);
+	//! Accessor for displaying J2000 Equatorial Line.
+	bool getFlagEquatorJ2000Line(void) const;
+	//! Get the current color of the J2000 Equatorial Line.
+	Vec3f getColorEquatorJ2000Line(void) const;
+	//! Set the color of the J2000 Equator Line.
+	//! @param newColor The color of J2000 equator line
+	//! @code
+	//! // example of usage in scripts
+	//! GridLinesMgr.setColorEquatorJ2000Line(Vec3f(1.0,0.0,0.0));
+	//! @endcode
+	void setColorEquatorJ2000Line(const Vec3f& newColor);
+
+	//! Setter for displaying Ecliptic of J2000 Line.
+	void setFlagEclipticJ2000Line(const bool displayed);
+	//! Accessor for displaying Ecliptic of J2000 Line.
+	bool getFlagEclipticJ2000Line(void) const;
+	//! Get the current color of the Ecliptic of J2000 Line.
+	Vec3f getColorEclipticJ2000Line(void) const;
+	//! Set the color of the Ecliptic of J2000 Line.
+	//! @param newColor The color of ecliptic 2000 line
+	//! @code
+	//! // example of usage in scripts
+	//! GridLinesMgr.setColorEcliptic2000Line(Vec3f(1.0,0.0,0.0));
+	//! @endcode
+	void setColorEclipticJ2000Line(const Vec3f& newColor);
+
 	//! Setter for displaying Ecliptic Line.
 	void setFlagEclipticLine(const bool displayed);
 	//! Accessor for displaying Ecliptic Line.
@@ -246,6 +342,20 @@
 	//! @endcode
 	void setColorEclipticLine(const Vec3f& newColor);
 
+	//! Setter for displaying precession circles.
+	void setFlagPrecessionCircles(const bool displayed);
+	//! Accessor for displaying precession circles.
+	bool getFlagPrecessionCircles(void) const;
+	//! Get the current color of the precession circles.
+	Vec3f getColorPrecessionCircles(void) const;
+	//! Set the color of the precession circles.
+	//! @param newColor The color of precession circles
+	//! @code
+	//! // example of usage in scripts
+	//! GridLinesMgr.setColorPrecessionCircles(Vec3f(1.0,0.0,0.0));
+	//! @endcode
+	void setColorPrecessionCircles(const Vec3f& newColor);
+
 	//! Setter for displaying Meridian Line.
 	void setFlagMeridianLine(const bool displayed);
 	//! Accessor for displaying Meridian Line.
@@ -291,12 +401,12 @@
 	//! Setter for displaying Galactic Equator Line.
 	void setFlagGalacticEquatorLine(const bool displayed);
 	//! @deprecated Setter for displaying Galactic "Plane" (i.e., Equator) Line. Left here for compatibility with older scripts.
-	//! @note will be delete in version 0.14
+	//! @note will be deleted in version 0.14
 	void setFlagGalacticPlaneLine(const bool displayed) { setFlagGalacticEquatorLine(displayed); }
 	//! Accessor for displaying Galactic Equator Line.
 	bool getFlagGalacticEquatorLine(void) const;
 	//! @deprecated Accessor for displaying Galactic "Plane" (i.e., Equator) Line. Left here for compatibility with older scripts.
-	//! @note will be delete in version 0.14
+	//! @note will be deleted in version 0.14
 	bool getFlagGalacticPlaneLine(void) const { return getFlagGalacticEquatorLine(); }
 	//! Get the current color of the Galactic Equator Line.
 	Vec3f getColorGalacticEquatorLine(void) const;
@@ -314,14 +424,22 @@
 	void equatorGridColorChanged(const Vec3f & newColor) const;
 	void equatorJ2000GridDisplayedChanged(const bool displayed) const;
 	void equatorJ2000GridColorChanged(const Vec3f & newColor) const;
+	void eclipticGridDisplayedChanged(const bool displayed) const;
+	void eclipticGridColorChanged(const Vec3f & newColor) const;
 	void eclipticJ2000GridDisplayedChanged(const bool displayed) const;
 	void eclipticJ2000GridColorChanged(const Vec3f & newColor) const;
 	void galacticGridDisplayedChanged(const bool displayed) const;
 	void galacticGridColorChanged(const Vec3f & newColor) const;
 	void equatorLineDisplayedChanged(const bool displayed) const;
 	void equatorLineColorChanged(const Vec3f & newColor) const;
+	void equatorJ2000LineDisplayedChanged(const bool displayed) const;
+	void equatorJ2000LineColorChanged(const Vec3f & newColor) const;
 	void eclipticLineDisplayedChanged(const bool displayed) const;
 	void eclipticLineColorChanged(const Vec3f & newColor) const;
+	void eclipticJ2000LineDisplayedChanged(const bool displayed) const;
+	void eclipticJ2000LineColorChanged(const Vec3f & newColor) const;
+	void precessionCirclesDisplayedChanged(const bool displayed) const;
+	void precessionCirclesColorChanged(const Vec3f & newColor) const;
 	void meridianLineDisplayedChanged(const bool displayed) const;
 	void meridianLineColorChanged(const Vec3f & newColor) const;
 	void longitudeLineDisplayedChanged(const bool displayed) const;
@@ -344,10 +462,15 @@
 	SkyGrid * equGrid;		// Equatorial grid
 	SkyGrid * equJ2000Grid;		// Equatorial J2000 grid
 	SkyGrid * galacticGrid;		// Galactic grid
+	SkyGrid * eclGrid;		// Ecliptic of Date grid
 	SkyGrid * eclJ2000Grid;		// Ecliptic J2000 grid
 	SkyGrid * aziGrid;		// Azimuthal grid
 	SkyLine * equatorLine;		// Celestial Equator line
+	SkyLine * equatorJ2000Line;	// Celestial Equator of J2000 line
 	SkyLine * eclipticLine;		// Ecliptic line
+	SkyLine * eclipticJ2000Line;	// Ecliptic line of J2000
+	SkyLine * precessionCircleN;	// Northern precession circle
+	SkyLine * precessionCircleS;	// Southern precession circle
 	SkyLine * meridianLine;		// Meridian line
 	SkyLine * longitudeLine; 	// Opposition/conjunction longitude line
 	SkyLine * horizonLine;		// Horizon line

=== modified file 'src/core/modules/Landscape.cpp'
--- src/core/modules/Landscape.cpp	2015-06-30 12:08:33 +0000
+++ src/core/modules/Landscape.cpp	2015-07-28 19:18:20 +0000
@@ -803,6 +803,7 @@
 	float y_baseImg_1 = sides[currentSide].texCoords[1]+ y_img_1*(sides[currentSide].texCoords[3]-sides[currentSide].texCoords[1]);
 	int y=(1.0-y_baseImg_1)*sidesImages[currentSide]->height();           // pixel Y from top.
 	QRgb pixVal=sidesImages[currentSide]->pixel(x, y);
+/*
 #ifndef NDEBUG
 	// GZ: please leave the comment available for further development!
 	qDebug() << "Oldstyle Landscape sampling: az=" << az*180.0 << "° alt=" << alt_rad*180.0f/M_PI
@@ -811,6 +812,7 @@
 			 << ", w=" << sidesImages[currentSide]->width() << " h=" << sidesImages[currentSide]->height()
 			 << " --> x:" << x << " y:" << y << " alpha:" << qAlpha(pixVal)/255.0f;
 #endif
+*/
 	return qAlpha(pixVal)/255.0f;
 }
 
@@ -1022,12 +1024,14 @@
 	int y= mapImage->height()/2*(1 + radius*std::cos(az));
 
 	QRgb pixVal=mapImage->pixel(x, y);
+/*
 #ifndef NDEBUG
 	// GZ: please leave the comment available for further development!
 	qDebug() << "Landscape sampling: az=" << (az+angleRotateZ)/M_PI*180.0f << "° alt=" << alt_rad/M_PI*180.f
 			 << "°, w=" << mapImage->width() << " h=" << mapImage->height()
 			 << " --> x:" << x << " y:" << y << " alpha:" << qAlpha(pixVal)/255.0f;
 #endif
+*/
 	return qAlpha(pixVal)/255.0f;
 
 
@@ -1210,6 +1214,7 @@
 	int x=(az_phot/2.0f) * mapImage->width(); // pixel X from left.
 
 	QRgb pixVal=mapImage->pixel(x, y);
+/*
 #ifndef NDEBUG
 	// GZ: please leave the comment available for further development!
 	qDebug() << "Landscape sampling: az=" << az*180.0 << "° alt=" << alt_pm1*90.0f
@@ -1217,6 +1222,7 @@
 			 << ", w=" << mapImage->width() << " h=" << mapImage->height()
 			 << " --> x:" << x << " y:" << y << " alpha:" << qAlpha(pixVal)/255.0f;
 #endif
+*/
 	return qAlpha(pixVal)/255.0f;
 
 }

=== modified file 'src/core/modules/Planet.cpp'
--- src/core/modules/Planet.cpp	2015-06-21 11:42:04 +0000
+++ src/core/modules/Planet.cpp	2015-07-28 19:18:20 +0000
@@ -24,7 +24,8 @@
 #include "StelSkyDrawer.hpp"
 #include "SolarSystem.hpp"
 #include "Planet.hpp"
-
+#include "planetsephems/precession.h"
+#include "StelObserver.hpp"
 #include "StelProjector.hpp"
 #include "sidereal_time.h"
 #include "StelTextureMgr.hpp"
@@ -225,15 +226,21 @@
 
 	oss << getPositionInfoString(core, flags);
 
-	if (flags&Extra)
-	{
-		static SolarSystem *ssystem=GETSTELMODULE(SolarSystem);
-		double ecl= ssystem->getEarth()->getRotObliquity(core->getJDay());
-		if (core->getCurrentLocation().planetName=="Earth")
-			oss << q_("Obliquity (of date, for Earth): %1").arg(StelUtils::radToDmsStr(ecl, true)) << "<br>";
-		//if (englishName!="Sun")
-		//	oss << q_("Obliquity (of date): %1").arg(StelUtils::radToDmsStr(getRotObliquity(core->getJDay()), true)) << "<br>";
-	}
+	// GZ This is mostly for debugging. Maybe also useful for letting people use our results to cross-check theirs, but we should not act as reference, currently...
+	// TODO: maybe separate this out into:
+	//if (flags&EclipticCoordXYZ)
+	// For now: add to EclipticCoord
+	//if (flags&EclipticCoord)
+	//	oss << q_("Ecliptical XYZ (VSOP87A): %1/%2/%3").arg(QString::number(eclipticPos[0], 'f', 3), QString::number(eclipticPos[1], 'f', 3), QString::number(eclipticPos[2], 'f', 3)) << "<br>";
+//	if (flags&Extra)
+//	{
+//		static SolarSystem *ssystem=GETSTELMODULE(SolarSystem);
+//		double ecl= ssystem->getEarth()->getRotObliquity(core->getJDay());
+//		if (core->getCurrentLocation().planetName=="Earth")
+//			oss << q_("Ecliptic obliquity (of date): %1").arg(StelUtils::radToDmsStr(ecl, true)) << "<br>";
+//		//if (englishName!="Sun")
+//		//	oss << q_("Obliquity (of date): %1").arg(StelUtils::radToDmsStr(getRotObliquity(core->getJDay()), true)) << "<br>";
+//	}
 
 	if (flags&Distance)
 	{
@@ -277,6 +284,10 @@
 	double siderealDay = getSiderealDay();
 	if (flags&Extra)
 	{
+		// This is a string you can activate for debugging. It shows the distance between observer and center of the body you are standing on.
+		// May be helpful for debugging critical parallax corrections for eclipses.
+		// For general use, find a better location first.
+		// oss << q_("Planetocentric distance &rho;: %1 (km)").arg(core->getCurrentObserver()->getDistanceFromCenter() * AU) <<"<br>";
 		if (siderealPeriod>0)
 		{
 			// TRANSLATORS: Sidereal (orbital) period for solar system bodies in days and in Julian years (symbol: a)
@@ -291,7 +302,7 @@
 				oss << q_("The period of rotation is chaotic") << "<br>";
 			}
 		}
-		if (englishName.compare("Sun")!=0)
+		if (englishName != "Sun")
 		{
 			const Vec3d& observerHelioPos = core->getObserverHeliocentricEclipticPos();
 			oss << QString(q_("Phase Angle: %1")).arg(StelUtils::radToDmsStr(getPhaseAngle(observerHelioPos))) << "<br>";
@@ -391,6 +402,10 @@
 	}
 }
 
+// return value in radians!
+// TODO: For earth, decide whether this should be Capitaine's omega_A (angle eclipticPoleJ2000//axis) or epsilon_A (angle axis//current ecliptic pole)
+// For now, it is epsilon_A, the angle between earth's rotational axis and mean ecliptic of date.
+// Details: e.g. Hilton etal, Report on Precession and the Ecliptic, Cel.Mech.Dyn.Astr.94:351-67 (2006), Fig1.
 double Planet::getRotObliquity(double JDay) const
 {
 	// JDay=2451545.0 for J2000.0
@@ -575,16 +590,36 @@
 
 }
 
-// Compute the transformation matrix from the local Planet coordinate to the parent Planet coordinate
+// Compute the transformation matrix from the local Planet coordinate system to the parent Planet coordinate system.
+// In case of the planets, this makes the axis point to the respective celestial pole.
+// TODO: Verify for the other planets if their axes are relative to J2000 ecliptic (VSOP87A XY plane) or relative to (precessed) ecliptic of date?
 void Planet::computeTransMatrix(double jd)
 {
+	// TODO: correct this for earth with the new model.
 	axisRotation = getSiderealTime(jd);
 
-	// Special case - heliocentric coordinates are on ecliptic,
+	// Special case - heliocentric coordinates are relative to eclipticJ2000 (VSOP87A XY plane),
 	// not solar equator...
+
 	if (parent)
 	{
-		rotLocalToParent = Mat4d::zrotation(re.ascendingNode - re.precessionRate*(jd-re.epoch)) * Mat4d::xrotation(re.obliquity);
+		// We can inject a proper precession plus even nutation matrix in this stage, if available.
+		if (englishName=="Earth")
+		  {
+			// rotLocalToParent = Mat4d::zrotation(re.ascendingNode - re.precessionRate*(jd-re.epoch)) * Mat4d::xrotation(-getRotObliquity(jd));
+			// GZ: We follow Capitaine's (2003) formulation P=Rz(Chi_A)*Rx(-omega_A)*Rz(-psi_A)*Rx(eps_o).
+			// ADS: 2011A&A...534A..22V = A&A 534, A22 (2011): Vondrak, Capitane, Wallace: New Precession Expressions, valid for long time intervals:
+			// See also Hilton et al, Report on Precession and the Ecliptic. Cel.Mech.Dyn.Astr. 94:351-367 (2006).
+			double eps_A, chi_A, omega_A, psi_A;
+			getPrecessionAnglesVondrak(jd, &eps_A, &chi_A, &omega_A, &psi_A);
+			// GZ This is the right combination for precession of the equator: Nodal rotation psi_A,
+			// then rotation by omega_A, the angle between EclPoleJ2000 and EarthPoleOfDate.
+			// The final rotation by chi_A rotates the equinox (zero degree).
+			// To achieve ecliptical coords of date, you just have now to add a rotX by epsilon_A (obliquity of date).
+			rotLocalToParent= Mat4d::zrotation(-psi_A) * Mat4d::xrotation(-omega_A) * Mat4d::zrotation(chi_A);
+		  }
+		else
+			rotLocalToParent = Mat4d::zrotation(re.ascendingNode - re.precessionRate*(jd-re.epoch)) * Mat4d::xrotation(re.obliquity);
 	}
 }
 
@@ -615,8 +650,17 @@
 double Planet::getSiderealTime(double jd) const
 {
 	if (englishName=="Earth")
-	{
-		return get_apparent_sidereal_time(jd);
+	{	// GZ I wanted to be sure that nutation is just those ignorable few arcseconds.
+		//qDebug() << "Difference apparent-mean sidereal times (s): " << (get_apparent_sidereal_time(jd)- get_mean_sidereal_time(jd))* 240.0; // 1degree=4min=240s.
+		// TODO: Reactivate Nutation (but following IAU-2000A) after fixing JD_UT/JD_ET issues, then change this call back to apparent_sidereal_time.
+		//return get_apparent_sidereal_time(jd);
+		return get_mean_sidereal_time(jd);
+
+		// In the newer precession/nutation literature (starting around 2006) there are two sets of algorithms:
+		// "Classical" sidereal time (Greenwich hour angle GHA) and a solution based on Earth Rotational Angle ERA.
+		// We keep using the classical set, but make sure we are correct!
+
+
 	}
 
 	double t = jd - re.epoch;
@@ -1801,7 +1845,7 @@
 	if (!re.siderealPeriod)
 		return;
 
-	const StelProjectorP prj = core->getProjection(StelCore::FrameHeliocentricEcliptic);
+	const StelProjectorP prj = core->getProjection(StelCore::FrameHeliocentricEclipticJ2000);
 
 	StelPainter sPainter(prj);
 
@@ -1812,7 +1856,7 @@
 	sPainter.setColor(orbitColor[0], orbitColor[1], orbitColor[2], orbitFader.getInterstate());
 	Vec3d onscreen;
 	// special case - use current Planet position as center vertex so that draws
-	// on it's orbit all the time (since segmented rather than smooth curve)
+	// on its orbit all the time (since segmented rather than smooth curve)
 	Vec3d savePos = orbit[ORBIT_SEGMENTS/2];
 	orbit[ORBIT_SEGMENTS/2]=getHeliocentricEclipticPos();
 	orbit[ORBIT_SEGMENTS]=orbit[0];

=== modified file 'src/core/modules/Planet.hpp'
--- src/core/modules/Planet.hpp	2015-04-17 21:30:03 +0000
+++ src/core/modules/Planet.hpp	2015-07-28 19:18:20 +0000
@@ -172,6 +172,8 @@
 	//! Get the radius of the planet in AU.
 	//! @return the radius of the planet in astronomical units.
 	double getRadius(void) const {return radius;}
+	//! Get the value (1-f) for oblateness f.
+	double getOneMinusOblateness(void) const {return oneMinusOblateness;}
 	//! Get duration of sidereal day
 	double getSiderealDay(void) const {return re.period;}
 	//! Get duration of sidereal year
@@ -219,6 +221,8 @@
 				 float _obliquity, float _ascendingNode,
 				 float _precessionRate, double _siderealPeriod);
 	double getRotAscendingnode(void) const {return re.ascendingNode;}
+	// return angle between axis and normal of ecliptic plane (or, for a moon, equatorial/reference plane defined by parent).
+	// TODO: decide if this is always angle between axis and J2000 ecliptic, or should be axis//current ecliptic!
 	double getRotObliquity(double JDay) const;
 
 	//! Get the Planet position in the parent Planet ecliptic coordinate in AU
@@ -321,8 +325,10 @@
 	Vec3f color;                     // exclusively used for drawing the planet halo
 
 	float albedo;                    // Planet albedo. Used for magnitude computation (but formula dubious!)
-	Mat4d rotLocalToParent;
-	float axisRotation;              // Rotation angle of the Planet on it's axis
+	Mat4d rotLocalToParent;          // GZ2015: was undocumented.
+					 // Apparently this is the axis orientation with respect to the parent body. For planets, this is axis orientation w.r.t. VSOP87A/J2000 ecliptical system.
+	float axisRotation;              // Rotation angle of the Planet on its axis.
+					 // For Earth, this should be Greenwich Mean Sidereal Time GMST.
 	StelTextureSP texMap;            // Planet map texture
 	StelTextureSP normalMap;         // Planet normal map texture
 
@@ -333,7 +339,7 @@
 	double lastJD;                   // caches JD of last positional computation
 	// The callback for the calculation of the equatorial rect heliocentric position at time JD.
 	posFuncType coordFunc;
-	void* userDataPtr;
+	void* userDataPtr;               // this is always used with an Orbit object.
 
 	OsculatingFunctType *const osculatingFunc;
 	QSharedPointer<Planet> parent;           // Planet parent i.e. sun for earth

=== modified file 'src/core/modules/SolarSystem.cpp'
--- src/core/modules/SolarSystem.cpp	2015-07-05 19:48:33 +0000
+++ src/core/modules/SolarSystem.cpp	2015-07-28 19:18:20 +0000
@@ -1691,6 +1691,10 @@
 	systemPlanets.clear();
 	// Memory leak? What's the proper way of cleaning shared pointers?
 
+	// Also delete Comet textures (loaded in loadPlanets()
+	Comet::tailTexture.clear();
+	Comet::comaTexture.clear();
+
 	// Re-load the ssystem.ini file
 	loadPlanets();	
 	computePositions(StelUtils::getJDFromSystem());

=== modified file 'src/core/planetsephems/elp82b.h'
--- src/core/planetsephems/elp82b.h	2010-04-15 12:28:34 +0000
+++ src/core/planetsephems/elp82b.h	2015-07-28 19:18:20 +0000
@@ -82,7 +82,7 @@
      
 
 #ifdef __cplusplus
-};
+}
 #endif
 
 #endif

=== modified file 'src/core/planetsephems/gust86.c'
--- src/core/planetsephems/gust86.c	2010-04-15 12:28:34 +0000
+++ src/core/planetsephems/gust86.c	2015-07-28 19:18:20 +0000
@@ -438,7 +438,7 @@
 static double gust86_jd0 = -1e100;
 static double gust86_elem[GUST86_DIM];
 
-void GetGust86Coor(double jd,int body,double *xyz) {
+void GetGust86Coor(const double jd,const int body,double *xyz) {
   GetGust86OsculatingCoor(jd,jd,body,xyz);
 }
 

=== modified file 'src/core/planetsephems/gust86.h'
--- src/core/planetsephems/gust86.h	2013-06-02 03:39:47 +0000
+++ src/core/planetsephems/gust86.h	2015-07-28 19:18:20 +0000
@@ -59,7 +59,7 @@
 #define GUST86_TITANIA   3
 #define GUST86_OBERON    4
 
-void GetGust86Coor(double jd,int body,double *xyz);
+void GetGust86Coor(const double jd, const int body, double *xyz);
   /* Return the rectangular coordinates of the given satellite
      and the given julian date jd expressed in dynamical time (TAI+32.184s).
      The origin of the xyz-coordinates is the center of the planet.
@@ -88,8 +88,8 @@
      ICRF <-> VSOP87 must be done with the matrix given above.
    */
      
-void GetGust86OsculatingCoor(const double jd0, const double jd, const int body,double *xyz);
-  /* The oculating orbit of epoch jd0, evatuated at jd, is returned.
+void GetGust86OsculatingCoor(const double jd0, const double jd, const int body, double *xyz);
+  /* The oculating orbit of epoch jd0, evaluated at jd, is returned.
   */
 
 #ifdef __cplusplus

=== added file 'src/core/planetsephems/precession.c'
--- src/core/planetsephems/precession.c	1970-01-01 00:00:00 +0000
+++ src/core/planetsephems/precession.c	2015-07-28 19:18:20 +0000
@@ -0,0 +1,260 @@
+/*
+Copyright (C) 2015 Georg Zotti
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Library General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335, USA.
+*/
+
+/*
+ * Precession solution following methods from:
+ * J. Vondrak, N. Capitaine, P. Wallace
+ * New precession expressions, valid for long time intervals
+ * Astronomy&Astrophysics 534, A22 (2011)
+ * DOI: 10.1051/0004-6361/201117274
+ * The data are only applicable for a time range of 200.000 years around J2000.
+ * This is by far enough for Stellarium as of 2015, but just to make sure I added a few asserts.
+ */
+
+#include <math.h>
+#include <assert.h>
+
+/* Interval threshold (days) for re-computing these values. with 1, compute only 1/day:  */
+#define PRECESSION_EPOCH_THRESHOLD 1.0
+
+/* cache results for retrieval if recomputation is not required */
+
+static double c_psi_A=0.0, c_omega_A=0.0, c_chi_A=0.0, /*c_p_A=0.0, */ c_epsilon_A=0.0,
+		c_Y_A=0.0, c_X_A=0.0, c_Q_A=0.0, c_P_A=0.0,
+		c_lastJDE=-1e100;
+
+static const double arcSec2Rad=M_PI*2.0/(360.0*3600.0);
+
+static const double PQvals[8][5]=
+{ //  1/Pn         P_A:Cn       Q_A:Cn        P_A:Sn        Q_A:Sn
+  { 1.0/ 708.15, -5486.751211, -684.661560,   667.666730, -5523.863691 },
+  { 1.0/2309.00,   -17.127623, 2446.283880, -2354.886252,  -549.747450 },
+  { 1.0/1620.00,  -617.517403,  399.671049,  -428.152441,  -310.998056 },
+  { 1.0/ 492.20,   413.442940, -356.652376,   376.202861,   421.535876 },
+  { 1.0/1183.00,    78.614193, -186.387003,   184.778874,   -36.776172 },
+  { 1.0/ 622.00,  -180.732815, -316.800070,   335.321713,  -145.278396 },
+  { 1.0/ 882.00,   -87.676083,  198.296071,  -185.138669,   -34.744450 },
+  { 1.0/ 547.00,    46.140315,  101.135679,  -120.972830,    22.885731 }};
+
+static const double XYvals[14][5]=
+{ //  1/Pn          Xa:Cn          Ya:Cn         Xa:Sn         Ya:Sn
+  { 1.0/ 256.75,  -819.940624,  75004.344875, 81491.287984,  1558.515853 },
+  { 1.0/ 708.15, -8444.676815,    624.033993,   787.163481,  7774.939698 },
+  { 1.0/ 274.20,  2600.009459,   1251.136893,  1251.296102, -2219.534038 },
+  { 1.0/ 241.45,  2755.175630,  -1102.212834, -1257.950837, -2523.969396 },
+  { 1.0/2309.00,  -167.659835,  -2660.664980, -2966.799730,   247.850422 },
+  { 1.0/ 492.20,   871.855056,    699.291817,   639.744522,  -846.485643 },
+  { 1.0/ 396.10,    44.769698,    153.167220,   131.600209, -1393.124055 },
+  { 1.0/ 288.90,  -512.313065,   -950.865637,  -445.040117,   368.526116 },
+  { 1.0/ 231.10,  -819.415595,    499.754645,   584.522874,   749.045012 },
+  { 1.0/1610.00,  -538.071099,   -145.188210,   -89.756563,   444.704518 },
+  { 1.0/ 620.00,  -189.793622,    558.116553,   524.429630,   235.934465 },
+  { 1.0/ 157.87,  -402.922932,    -23.923029,   -13.549067,   374.049623 },
+  { 1.0/ 220.30,   179.516345,   -165.405086,  -210.157124,  -171.330180 },
+  { 1.0/1200.00,    -9.814756,      9.344131,   -44.919798,   -22.899655 }};
+
+
+static const double precVals[18][7]=
+{ // 1/Pn         psi_A:Cn       om_A:Cn       chi_A:Cn         psi_A:Sn       om_A:Sn       chi_A:Sn
+
+  { 1.0/402.90,  -22206.325946,  1267.727824, -13765.924050,    -3243.236469, -8571.476251,  -2206.967126 },
+  { 1.0/256.75,   12236.649447,  1702.324248,  13511.858383,    -3969.723769,  5309.796459,  -4186.752711 },
+  { 1.0/292.00,   -1589.008343, -2970.553839,  -1455.229106,     7099.207893,  -610.393953,   6737.949677 },
+  { 1.0/537.22,    2482.103195,   693.790312,   1054.394467,    -1903.696711,   923.201931,   -856.922846 },
+  { 1.0/241.45,     150.322920,   -14.724451,      0.0     ,      146.435014,     3.759055,      0.0      },
+  { 1.0/375.22,     -13.632066,  -516.649401,   -112.300144,     1300.630106,   -40.691114,    957.149088 },
+  { 1.0/157.87,     389.437420,  -356.794454,    202.769908,     1727.498039,    80.437484,   1709.440735 },
+  { 1.0/274.20,    2031.433792,  -129.552058,   1936.050095,      299.854055,   807.300668,    154.425505 },
+  { 1.0/203.00,     363.748303,   256.129314,      0.0     ,    -1217.125982,    83.712326,      0.0      },
+  { 1.0/440.00,    -896.747562,   190.266114,   -655.484214,     -471.367487,  -368.654854,   -243.520976 },
+  { 1.0/170.72,    -926.995700,    95.103991,   -891.898637,     -441.682145,  -191.881064,   -406.539008 },
+  { 1.0/713.37,      37.070667,  -332.907067,      0.0     ,      -86.169171,    -4.263770,      0.0      },
+  { 1.0/313.00,    -597.682468,   131.337633,      0.0     ,     -308.320429,  -270.353691,      0.0      },
+  { 1.0/128.38,      66.282812,    82.731919,   -333.322021,     -422.815629,    11.602861,   -446.656435 },
+  { 1.0/202.00,       0.0     ,     0.0     ,    327.517465,        0.0     ,     0.0     ,  -1049.071786 },
+  { 1.0/315.00,       0.0     ,     0.0     ,   -494.780332,        0.0     ,     0.0     ,   -301.504189 },
+  { 1.0/136.32,       0.0     ,     0.0     ,    585.492621,        0.0     ,     0.0     ,     41.348740 },
+  { 1.0/490.00,       0.0     ,     0.0     ,    110.512834,        0.0     ,     0.0     ,    142.525186 }};
+
+static const double p_epsVals[10][5]=
+{ //  1/Pn         p_A:Cn     eps_A:Cn        p_A:Sn      eps_A:Sn
+  { 1.0/ 409.90, -6908.287473,  753.872780, -2845.175469, -1704.720302},
+  { 1.0/ 396.15, -3198.706291, -247.805823,   449.844989,  -862.308358},
+  { 1.0/ 537.22,  1453.674527,  379.471484, -1255.915323,   447.832178},
+  { 1.0/ 402.90,  -857.748557,  -53.880558,   886.736783,  -889.571909},
+  { 1.0/ 417.15,  1173.231614,  -90.109153,   418.887514,   190.402846},
+  { 1.0/ 288.92,  -156.981465, -353.600190,   997.912441,   -56.564991},
+  { 1.0/4043.00,   371.836550,  -63.115353,  -240.979710,  -296.222622},
+  { 1.0/ 306.00,  -216.619040,  -28.248187,    76.541307,   -75.859952},
+  { 1.0/ 277.00,   193.691479,   17.703387,   -36.788069,    67.473503},
+  { 1.0/ 203.00,    11.891524,   38.911307,  -170.964086,     3.014055}};
+
+// compute angles for the series we are in fact using.
+// jde: date JD_TT
+// 
+void getPrecessionAnglesVondrak(const double jde, double *epsilon_A, double *chi_A, double *omega_A, double *psi_A)
+{
+	if (fabs(jde-c_lastJDE) > PRECESSION_EPOCH_THRESHOLD)
+	{
+		double T=(jde-2451545.0)* (1.0/36525.0); // Julian centuries from J2000.0
+		assert(fabs(T)<=2000); // MAKES SURE YOU NEVER OVERSTRETCH THIS!
+		double T2pi= T*(2.0*M_PI); // Julian centuries from J2000.0, premultiplied by 2Pi
+		// these are actually small greek letters in the papers.
+		double Psi_A=0.0;
+		double Omega_A=0.0;
+		double Chi_A=0.0;
+		double Epsilon_A=0.0;
+		//double p_A=0.0; // currently unused. The data don't disturb.
+		int i;
+		for (i=0; i<18; ++i)
+		{
+			double invP=precVals[i][0];
+			double sin2piT_P, cos2piT_P;
+#ifdef _GNU_SOURCE
+			sincos(T2pi*invP, &sin2piT_P, &cos2piT_P);
+#else
+			double phase=T2pi*invP;
+			sin2piT_P= sin(phase);
+			cos2piT_P= cos(phase);
+#endif
+			Psi_A   += precVals[i][1]*cos2piT_P + precVals[i][4]*sin2piT_P;
+			Omega_A += precVals[i][2]*cos2piT_P + precVals[i][5]*sin2piT_P;
+			Chi_A   += precVals[i][3]*cos2piT_P + precVals[i][6]*sin2piT_P;
+		}
+
+		for (i=0; i<10; ++i)
+		{
+			double invP=p_epsVals[i][0];
+			double sin2piT_P, cos2piT_P;
+#ifdef _GNU_SOURCE
+			sincos(T2pi*invP, &sin2piT_P, &cos2piT_P);
+#else
+			double phase=T2pi*invP;
+			sin2piT_P= sin(phase);
+			cos2piT_P= cos(phase);
+#endif
+			//p_A       += p_epsVals[i][1]*cos2piT_P + p_epsVals[i][3]*sin2piT_P;
+			Epsilon_A += p_epsVals[i][2]*cos2piT_P + p_epsVals[i][4]*sin2piT_P;
+		}
+
+		Psi_A     += (( 289.e-9*T - 0.00740913)*T + 5042.7980307)*T +  8473.343527;
+		Omega_A   += (( 151.e-9*T + 0.00000146)*T -    0.4436568)*T + 84283.175915;
+		Chi_A     += (( -61.e-9*T + 0.00001472)*T +    0.0790159)*T -    19.657270;
+		//p_A       += ((271.e-9*T - 0.00710733)*T + 5043.0520035)*T +  8134.017132;
+		Epsilon_A += ((-110.e-9*T - 0.00004039)*T +    0.3624445)*T + 84028.206305;
+		c_psi_A     = arcSec2Rad*Psi_A;
+		c_omega_A   = arcSec2Rad*Omega_A;
+		c_chi_A     = arcSec2Rad*Chi_A;
+		// c_p_A     = arcSec2Rad*p_A;
+		c_epsilon_A = arcSec2Rad*Epsilon_A;
+	}
+	*psi_A     = c_psi_A;
+	*omega_A   = c_omega_A;
+	*chi_A     = c_chi_A;
+	*epsilon_A = c_epsilon_A;
+}
+
+void getPrecessionAnglesVondrakPQXYe(const double jde, double *vP_A, double *vQ_A, double *vX_A, double *vY_A, double *vepsilon_A)
+{
+	if (fabs(jde-c_lastJDE) > PRECESSION_EPOCH_THRESHOLD)
+	{
+		double T=(jde-2451545.0)* (1.0/36525.0);
+		assert(fabs(T)<=2000); // MAKES SURE YOU NEVER OVERSTRETCH THIS!
+		double T2pi= T*(2.0*M_PI); // Julian centuries from J2000.0, premultiplied by 2Pi
+		// these are actually small greek letters in the papers.
+		double P_A=0.0;
+		double Q_A=0.0;
+		double X_A=0.0;
+		double Y_A=0.0;
+		double Epsilon_A=0.0;
+		int i;
+		for (i=0; i<8; ++i)
+		{
+			double invP=PQvals[i][0];
+			double sin2piT_P, cos2piT_P;
+#ifdef _GNU_SOURCE
+			sincos(T2pi*invP, &sin2piT_P, &cos2piT_P);
+#else
+			double phase=T2pi*invP;
+			sin2piT_P= sin(phase);
+			cos2piT_P= cos(phase);
+#endif
+			P_A += PQvals[i][1]*cos2piT_P + PQvals[i][3]*sin2piT_P;
+			Q_A += PQvals[i][2]*cos2piT_P + PQvals[i][4]*sin2piT_P;
+		}
+		for (i=0; i<14; ++i)
+		{
+			double invP=XYvals[i][0];
+			double sin2piT_P, cos2piT_P;
+#ifdef _GNU_SOURCE
+			sincos(T2pi*invP, &sin2piT_P, &cos2piT_P);
+#else
+			double phase=T2pi*invP;
+			sin2piT_P= sin(phase);
+			cos2piT_P= cos(phase);
+#endif
+			X_A += XYvals[i][1]*cos2piT_P + XYvals[i][3]*sin2piT_P;
+			Y_A += XYvals[i][2]*cos2piT_P + XYvals[i][4]*sin2piT_P;
+		}
+		for (i=0; i<10; ++i)
+		{
+			double invP=p_epsVals[i][0];
+			double sin2piT_P, cos2piT_P;
+#ifdef _GNU_SOURCE
+			sincos(T2pi*invP, &sin2piT_P, &cos2piT_P);
+#else
+			double phase=T2pi*invP;
+			sin2piT_P= sin(phase);
+			cos2piT_P= cos(phase);
+#endif
+			//p_A       += p_epsVals[i][1]*cos2piT_P + p_epsVals[i][3]*sin2piT_P;
+			Epsilon_A += p_epsVals[i][2]*cos2piT_P + p_epsVals[i][4]*sin2piT_P;
+		}
+
+		// Now the polynomial terms in T. Horner's scheme is best again.
+		P_A       += (( 110.e-9*T - 0.00028913)*T -    0.1189000)*T +  5851.607687;
+		Q_A       += ((-437.e-9*T - 0.00000020)*T +    1.1689818)*T -  1600.886300;
+		X_A       += ((-152.e-9*T - 0.00037173)*T +    0.4252841)*T +  5453.282155;
+		Y_A       += ((+231.e-9*T - 0.00018725)*T -    0.7675452)*T - 73750.930350;
+		Epsilon_A += (( 110.e-9*T - 0.00004039)*T +    0.3624445)*T + 84028.206305;
+		c_P_A       = arcSec2Rad*P_A;
+		c_Q_A       = arcSec2Rad*Q_A;
+		c_X_A       = arcSec2Rad*X_A;
+		c_Y_A       = arcSec2Rad*Y_A;
+		c_epsilon_A = arcSec2Rad*Epsilon_A;
+	}
+	*vP_A       = c_P_A;
+	*vQ_A       = c_Q_A;
+	*vX_A       = c_X_A;
+	*vY_A       = c_Y_A;
+	*vepsilon_A = c_epsilon_A;
+
+}
+
+//! Just return (presumably precomputed) ecliptic obliquity.
+double getPrecessionAngleVondrakEpsilon(const double jde)
+{
+	double epsilon_A, dummy_chi_A, dummy_omega_A, dummy_psi_A;
+	getPrecessionAnglesVondrak(jde, &epsilon_A, &dummy_chi_A, &dummy_omega_A, &dummy_psi_A);
+	return epsilon_A;
+}
+//! Just return (presumably precomputed) ecliptic obliquity.
+double getPrecessionAngleVondrakCurrentEpsilonA(void)
+{
+	return c_epsilon_A;
+}

=== added file 'src/core/planetsephems/precession.h'
--- src/core/planetsephems/precession.h	1970-01-01 00:00:00 +0000
+++ src/core/planetsephems/precession.h	2015-07-28 19:18:20 +0000
@@ -0,0 +1,59 @@
+/*
+Copyright (C) 2015 Georg Zotti
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Library General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335, USA.
+*/
+#ifndef _PRECESSION_H_
+#define _PRECESSION_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+//! Precession modelled from:
+//! J. Vondrák, N. Capitaine, and P. Wallace: New precession expressions, valid for long time intervals
+//! A&A (Astronomy&Astrophysics) 534, A22 (2011)
+//! DOI: http://dx.doi.org/10.1051/0004-6361/201117274
+//! This paper describes a precession model valid for +/-200.000 years from J2000.0 and consistent with P03 precession accepted as IAU2006 Precession.
+//! Some better understanding of the angles can be found in:
+//! + 1994AJ____108__711W J.G.Williams: Contributions to the Earth's Obliquity Rate, Precession and Nutation (Angles of eq. (35))
+//! + A&A 459, 981–985 (2006) DOI: 10.1051/0004-6361:20065897: Wallace&Capitaine: Precession-nutation procedures consistent with IAU 2006 resolutions
+//!
+//! The angles computed therein are used to rotate the planet Earth's axis, and also to rotate an "Ecliptic of Date", i.e. the current orbital plane of Earth.
+//! Currently this is without Nutation.
+//! Return values are in radians
+void getPrecessionAnglesVondrak(const double jde, double *epsilon_A, double *chi_A, double *omega_A, double *psi_A);
+
+//! Alternative solution, the one also implemented in the paper,
+//! combining matrix P from P_A, Q_A, X_A, Y_A and, for the ecliptic of date, rotate back by epsilon_A.
+//! Return values are in radians.
+//! This solution is currently unused, it seems easier to use the Capitaine sequence above.
+void getPrecessionAnglesVondrakPQXYe(const double jde, double *vP_A, double *vQ_A, double *vX_A, double *vY_A, double *vepsilon_A);
+
+//! Return ecliptic obliquity. [radians]
+double getPrecessionAngleVondrakEpsilon(const double jde);
+
+//! Just return (previously computed) ecliptic obliquity. [radians]
+double getPrecessionAngleVondrakCurrentEpsilonA(void);
+
+//! TODO: To complete the task of correct&accurate precession-nutation handling, find IAU-2000A Nutation and how this fits in here.
+//! E.g. A&A 459, 981–985 (2006) P. T. Wallace and N. Capitaine: Precession-nutation procedures consistent with IAU 2006 resolutions. DOI: 10.1051/0004-6361:20065897
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

=== modified file 'src/core/planetsephems/sidereal_time.c'
--- src/core/planetsephems/sidereal_time.c	2014-02-05 16:51:48 +0000
+++ src/core/planetsephems/sidereal_time.c	2015-07-28 19:18:20 +0000
@@ -18,6 +18,8 @@
 */
 
 #include <math.h>
+#include <assert.h>
+#include "precession.h"
 
 #ifndef M_PI
 #define M_PI           3.14159265358979323846
@@ -44,7 +46,7 @@
 #define LN_NUTATION_EPOCH_THRESHOLD 0.1
 
 
-/* Nutation is a period oscillation of the Earths rotational axis around it's mean position.*/
+/* Nutation is a periodic oscillation of the Earth's rotational axis around its mean position.*/
 
 /*
  Contains Nutation in longitude, obliquity and ecliptic obliquity.
@@ -52,9 +54,9 @@
 */
 struct ln_nutation
 {
-	double longitude;	/*!< Nutation in longitude */
-	double obliquity;	/*!< Nutation in obliquity */
-	double ecliptic;	/*!< Obliquity of the ecliptic */
+	double deltaPsi;	/*!< DeltaPsi, Nutation in longitude */
+	double deltaEps;	/*!< DeltaEps, Nutation in obliquity */
+	double ecliptic;	/*!< epsilon, Mean Obliquity of the ecliptic */
 };
 
 struct nutation_arguments
@@ -215,6 +217,8 @@
 * Meeus, Astr. Alg. (1st ed., 1994), Chapter 21 pg 131-134 Using Table 21A */
 /* GZ: Changed: ecliptic obliquity used to be constant J2000.0. 
  * If you don't compute this, you may as well forget about nutation!
+ * 2015: Laskar's 1986 formula replaced by Vondrak 2011. c_ecliptic is now epsilon_A, Vondrak's obliquity of date.
+ * TODO: replace this whole function with Nutation IAU2000A or compatible version.
  */
 void get_nutation (double JD, struct ln_nutation * nutation)
 {
@@ -245,7 +249,7 @@
 		F = 93.2719100 + 483202.017538 * T - 0.0036825 * T2 + T3 / 327270.0;
 		O = 125.04452 - 1934.136261 * T + 0.0020708 * T2 + T3 / 450000.0;
 
-		/ * GZotti: Laskar's formula, only valid for J2000+/-10000 years! */
+		/ * GZotti: Laskar's formula (1986), only valid for J2000+/-10000 years! */
 		if (fabs(T)<100) 
 		  {
 		    double U=T/100.0;	
@@ -322,25 +326,32 @@
 	  }
 
 	/* return results */
-	nutation->longitude = c_longitude;
-	nutation->obliquity = c_obliquity;
+	nutation->deltaPsi = c_longitude;
+	nutation->deltaEps = c_obliquity;
 	nutation->ecliptic = c_ecliptic;
 }
 
-/* Calculate the mean sidereal time at the meridian of Greenwich of a given date.
- * returns apparent sidereal time (degree).
- * Formula 11.1, 11.4 pg 83 */
+/* Calculate the mean sidereal time at the meridian of Greenwich (GMST) of a given date.
+ * returns mean sidereal time (degrees).
+ * Formula 11.1, 11.4 pg 83
+ * MAKE SURE argument JD is UT, not TT!
+ */
 double get_mean_sidereal_time (double JD)
 {
 	double sidereal;
-	double T;
+	double T, T1;
     
-	T = (JD - 2451545.0) / 36525.0;
+
+	T1 = (JD - 2451545.0);
+	T= T1 * (1.0/ 36525.0);
         
 	/* calc mean angle */
-	sidereal = 280.46061837 + (360.98564736629 * (JD - 2451545.0)) + (0.000387933 * T * T) - (T * T * T / 38710000.0);
+	//sidereal = 280.46061837 + (360.98564736629 * (JD - 2451545.0)) + (0.000387933 * T * T) - (T * T * T / 38710000.0);
     
-	/* add a convenient multiple of 360 degrees */
+	sidereal = range_degrees(T1*360.98564736629); // Number gets large, better bring that to interval soon.
+	sidereal += (-1.0/38710000.0 * T + 0.000387933)*T*T+280.46061837;
+
+	/* add again a convenient multiple of 360 degrees */
 	sidereal = range_degrees (sidereal);
 
 	return sidereal;
@@ -348,13 +359,15 @@
 
 
 /* Calculate the apparent sidereal time at the meridian of Greenwich of a given date.
- * returns apparent sidereal time (degree).
+ * returns apparent sidereal time (degrees).
  * Formula 11.1, 11.4 pg 83 */
 double get_apparent_sidereal_time (double JD)
 {
 	double correction, sidereal;
 	struct ln_nutation nutation;
    
+	// GZ For now this is forbidden!
+	//assert(0);
 	/* get the mean sidereal time */
 	sidereal = get_mean_sidereal_time (JD);
         
@@ -363,23 +376,25 @@
 	get_nutation (JD, &nutation);
     
 	/* GZ: This was the only place where this was used. I added the summation here. */
-	correction = (nutation.longitude * cos ((nutation.ecliptic+nutation.obliquity)*M_PI/180.));
+	correction = (nutation.deltaPsi * cos ((nutation.ecliptic+nutation.deltaEps)*M_PI/180.));
 
 	sidereal += correction;
    
 	return (sidereal);
 }
 
+// return value in degrees
 double get_mean_ecliptical_obliquity(double JDE)
 {
-	struct ln_nutation nutation;
-	get_nutation(JDE, &nutation);
-	return nutation.ecliptic;
+//	struct ln_nutation nutation;
+//	get_nutation(JDE, &nutation);
+//	return nutation.ecliptic;
+	return getPrecessionAngleVondrakEpsilon(JDE)*180.0/M_PI;
 }
 
 double get_nutation_longitude(double JDE)
 {
 	struct ln_nutation nutation;
 	get_nutation(JDE, &nutation);
-	return nutation.longitude;
+	return nutation.deltaPsi;
 }

=== modified file 'src/core/planetsephems/vsop87.h'
--- src/core/planetsephems/vsop87.h	2013-06-02 03:39:47 +0000
+++ src/core/planetsephems/vsop87.h	2015-07-28 19:18:20 +0000
@@ -69,7 +69,7 @@
   */
 
 void GetVsop87OsculatingCoor(const double jd0,const double jd, const int body,double *xyz);
-  /* The oculating orbit of epoch jd0, evatuated at jd, is returned.
+  /* The oculating orbit of epoch jd0, evaluated at jd, is returned.
   */
 
 #ifdef __cplusplus

=== modified file 'src/gui/ConfigurationDialog.cpp'
--- src/gui/ConfigurationDialog.cpp	2015-07-08 13:31:50 +0000
+++ src/gui/ConfigurationDialog.cpp	2015-07-28 19:18:20 +0000
@@ -563,13 +563,16 @@
 	// view dialog / markings tab settings
 	conf->setValue("viewing/flag_azimuthal_grid", glmgr->getFlagAzimuthalGrid());
 	conf->setValue("viewing/flag_equatorial_grid", glmgr->getFlagEquatorGrid());
+	conf->setValue("viewing/flag_equatorial_J2000_grid", glmgr->getFlagEquatorJ2000Grid());
 	conf->setValue("viewing/flag_equator_line", glmgr->getFlagEquatorLine());
+	conf->setValue("viewing/flag_equator_J2000_line", glmgr->getFlagEquatorJ2000Line());
 	conf->setValue("viewing/flag_ecliptic_line", glmgr->getFlagEclipticLine());
+	conf->setValue("viewing/flag_ecliptic_J2000_line", glmgr->getFlagEclipticJ2000Line());
+	conf->setValue("viewing/flag_ecliptic_grid", glmgr->getFlagEclipticGrid());
 	conf->setValue("viewing/flag_ecliptic_J2000_grid", glmgr->getFlagEclipticJ2000Grid());
 	conf->setValue("viewing/flag_meridian_line", glmgr->getFlagMeridianLine());
 	conf->setValue("viewing/flag_longitude_line", glmgr->getFlagLongitudeLine());
 	conf->setValue("viewing/flag_horizon_line", glmgr->getFlagHorizonLine());
-	conf->setValue("viewing/flag_equatorial_J2000_grid", glmgr->getFlagEquatorJ2000Grid());
 	conf->setValue("viewing/flag_galactic_grid", glmgr->getFlagGalacticGrid());
 	conf->setValue("viewing/flag_galactic_equator_line", glmgr->getFlagGalacticEquatorLine());
 	conf->setValue("viewing/flag_cardinal_points", lmgr->getFlagCardinalsPoints());

=== modified file 'src/gui/LocationDialog.cpp'
--- src/gui/LocationDialog.cpp	2014-11-25 13:02:40 +0000
+++ src/gui/LocationDialog.cpp	2015-07-28 19:18:20 +0000
@@ -340,7 +340,7 @@
 	else
 		loc.planetName = ui->planetNameComboBox->itemData(index).toString();
 	loc.name = ui->cityNameLineEdit->text();
-	loc.latitude = ui->latitudeSpinBox->valueDegrees();
+	loc.latitude = qMin(90.0, qMax(-90.0, ui->latitudeSpinBox->valueDegrees()));
 	loc.longitude = ui->longitudeSpinBox->valueDegrees();
 	loc.altitude = ui->altitudeSpinBox->value();
 	index = ui->countryNameComboBox->currentIndex();

=== modified file 'src/gui/ViewDialog.cpp'
--- src/gui/ViewDialog.cpp	2015-07-10 09:38:01 +0000
+++ src/gui/ViewDialog.cpp	2015-07-28 19:18:20 +0000
@@ -271,7 +271,9 @@
 
 	// Grid and lines
 	connectCheckBox(ui->showEquatorLineCheckBox, "actionShow_Equator_Line");
-	connectCheckBox(ui->showEclipticLineCheckBox, "actionShow_Ecliptic_Line");
+	connectCheckBox(ui->showEquatorJ2000LineCheckBox, "actionShow_Equator_J2000_Line");
+	connectCheckBox(ui->showEclipticLineJ2000CheckBox, "actionShow_Ecliptic_J2000_Line");
+	connectCheckBox(ui->showEclipticLineOfDateCheckBox, "actionShow_Ecliptic_Line");
 	connectCheckBox(ui->showMeridianLineCheckBox, "actionShow_Meridian_Line");
 	connectCheckBox(ui->showLongitudeLineCheckBox, "actionShow_Longitude_Line");
 	connectCheckBox(ui->showHorizonLineCheckBox, "actionShow_Horizon_Line");
@@ -281,7 +283,9 @@
 	connectCheckBox(ui->showAzimuthalGridCheckBox, "actionShow_Azimuthal_Grid");
 	connectCheckBox(ui->showEquatorialJ2000GridCheckBox, "actionShow_Equatorial_J2000_Grid");
 	connectCheckBox(ui->showEclipticGridJ2000CheckBox, "actionShow_Ecliptic_J2000_Grid");
+	connectCheckBox(ui->showEclipticGridOfDateCheckBox, "actionShow_Ecliptic_Grid");
 	connectCheckBox(ui->showCardinalPointsCheckBox, "actionShow_Cardinal_Points");
+	connectCheckBox(ui->showPrecessionCirclesCheckBox, "actionShow_Precession_Circles");
 
 	// Constellations
 	ConstellationMgr* cmgr = GETSTELMODULE(ConstellationMgr);

=== modified file 'src/gui/viewDialog.ui'
--- src/gui/viewDialog.ui	2015-07-10 09:38:01 +0000
+++ src/gui/viewDialog.ui	2015-07-28 19:18:20 +0000
@@ -1453,27 +1453,49 @@
                 <layout class="QVBoxLayout" name="verticalLayout_13">
                  <item>
                   <widget class="QCheckBox" name="showEquatorialJ2000GridCheckBox">
+                   <property name="toolTip">
+                    <string>Equatorial coordinates of J2000.0.</string>
+                   </property>
                    <property name="text">
-                    <string>Equatorial grid (on J2000)</string>
+                    <string>Equatorial grid (J2000)</string>
                    </property>
                   </widget>
                  </item>
                  <item>
                   <widget class="QCheckBox" name="showEquatorialGridCheckBox">
+                   <property name="toolTip">
+                    <string>Equatorial coordinates of current date and planet.</string>
+                   </property>
                    <property name="text">
-                    <string>Equatorial grid (on date)</string>
+                    <string>Equatorial grid (of date)</string>
                    </property>
                   </widget>
                  </item>
                  <item>
                   <widget class="QCheckBox" name="showEclipticGridJ2000CheckBox">
-                   <property name="text">
-                    <string>Ecliptic grid (on J2000)</string>
+                   <property name="toolTip">
+                    <string>Ecliptical coordinates for J2000.0.</string>
+                   </property>
+                   <property name="text">
+                    <string>Ecliptic grid (J2000)</string>
+                   </property>
+                  </widget>
+                 </item>
+                 <item>
+                  <widget class="QCheckBox" name="showEclipticGridOfDateCheckBox">
+                   <property name="toolTip">
+                    <string>Ecliptical coordinates for current date. Displayed on Earth only.</string>
+                   </property>
+                   <property name="text">
+                    <string>Ecliptic grid (of date)</string>
                    </property>
                   </widget>
                  </item>
                  <item>
                   <widget class="QCheckBox" name="showAzimuthalGridCheckBox">
+                   <property name="toolTip">
+                    <string>Altitudes and azimuth (counted from North towards East).</string>
+                   </property>
                    <property name="text">
                     <string>Azimuthal grid</string>
                    </property>
@@ -1481,6 +1503,9 @@
                  </item>
                  <item>
                   <widget class="QCheckBox" name="showGalacticGridCheckBox">
+                   <property name="toolTip">
+                    <string>Galactic Coordinates, System II (IAU 1958).</string>
+                   </property>
                    <property name="text">
                     <string>Galactic grid</string>
                    </property>
@@ -1488,49 +1513,72 @@
                  </item>
                  <item>
                   <widget class="QCheckBox" name="showCardinalPointsCheckBox">
+                   <property name="toolTip">
+                    <string>Labels for the Cardinal directions.</string>
+                   </property>
                    <property name="text">
                     <string>Cardinal points</string>
                    </property>
                   </widget>
                  </item>
+                 <item>
+                  <widget class="QCheckBox" name="showPrecessionCirclesCheckBox">
+                   <property name="toolTip">
+                    <string>Instantaneous circles of earth's axis on its motion around ecliptical poles. Displayed on Earth only.</string>
+                   </property>
+                   <property name="text">
+                    <string>Precession circles</string>
+                   </property>
+                  </widget>
+                 </item>
                 </layout>
                </item>
                <item>
                 <layout class="QVBoxLayout" name="verticalLayout_15">
                  <item>
+                  <widget class="QCheckBox" name="showEquatorJ2000LineCheckBox">
+                   <property name="toolTip">
+                    <string>Show celestial equator of J2000.0.</string>
+                   </property>
+                   <property name="text">
+                    <string>Equator (J2000)</string>
+                   </property>
+                  </widget>
+                 </item>
+                 <item>
                   <widget class="QCheckBox" name="showEquatorLineCheckBox">
                    <property name="toolTip">
-                    <string>Show equator line</string>
-                   </property>
-                   <property name="text">
-                    <string>Equator</string>
-                   </property>
-                  </widget>
-                 </item>
-                 <item>
-                  <widget class="QCheckBox" name="showMeridianLineCheckBox">
-                   <property name="toolTip">
-                    <string>Show meridian line</string>
-                   </property>
-                   <property name="text">
-                    <string>Meridian</string>
-                   </property>
-                  </widget>
-                 </item>
-                 <item>
-                  <widget class="QCheckBox" name="showEclipticLineCheckBox">
-                   <property name="toolTip">
-                    <string>Show ecliptic line</string>
-                   </property>
-                   <property name="text">
-                    <string>Ecliptic</string>
+                    <string>Show celestial equator of current planet and date.</string>
+                   </property>
+                   <property name="text">
+                    <string>Equator (of date)</string>
+                   </property>
+                  </widget>
+                 </item>
+                 <item>
+                  <widget class="QCheckBox" name="showEclipticLineJ2000CheckBox">
+                   <property name="toolTip">
+                    <string>Show ecliptic line of J2000.0 (VSOP87A fundamental plane).</string>
+                   </property>
+                   <property name="text">
+                    <string>Ecliptic (J2000)</string>
+                   </property>
+                  </widget>
+                 </item>
+                 <item>
+                  <widget class="QCheckBox" name="showEclipticLineOfDateCheckBox">
+                   <property name="toolTip">
+                    <string>Show ecliptic line of current date.</string>
+                   </property>
+                   <property name="text">
+                    <string>Ecliptic (of date)</string>
                    </property>
                   </widget>
                  </item>
                  <item>
                   <widget class="QCheckBox" name="showHorizonLineCheckBox">
                    <property name="toolTip">
-                    <string>Show horizon line</string>
+                    <string>Show horizon line.</string>
                    </property>
                    <property name="text">
                     <string>Horizon</string>
@@ -1540,7 +1588,7 @@
                  <item>
                   <widget class="QCheckBox" name="showGalacticEquatorLineCheckBox">
                    <property name="toolTip">
-                    <string>Show Galactic equator line</string>
+                    <string>Show Galactic equator line.</string>
                    </property>
                    <property name="text">
                     <string>Galactic equator</string>
@@ -1548,6 +1596,16 @@
                   </widget>
                  </item>
                  <item>
+                  <widget class="QCheckBox" name="showMeridianLineCheckBox">
+                   <property name="toolTip">
+                    <string>Show meridian line.</string>
+                   </property>
+                   <property name="text">
+                    <string>Meridian</string>
+                   </property>
+                  </widget>
+                 </item>
+                 <item>
                   <widget class="QCheckBox" name="showLongitudeLineCheckBox">
                    <property name="toolTip">
                     <string>Opposition/conjunction longitude line - the line of ecliptic longitude which passes through both ecliptic poles, the Sun and opposition point.</string>
@@ -2219,8 +2277,7 @@
   <tabstop>showAzimuthalGridCheckBox</tabstop>
   <tabstop>showGalacticGridCheckBox</tabstop>
   <tabstop>showEquatorLineCheckBox</tabstop>
-  <tabstop>showMeridianLineCheckBox</tabstop>
-  <tabstop>showEclipticLineCheckBox</tabstop>
+  <tabstop>showEclipticLineOfDateCheckBox</tabstop>
   <tabstop>showHorizonLineCheckBox</tabstop>
   <tabstop>showGalacticEquatorLineCheckBox</tabstop>
   <tabstop>showConstellationLinesCheckBox</tabstop>

=== added file 'src/tests/testPrecession.cpp'
--- src/tests/testPrecession.cpp	1970-01-01 00:00:00 +0000
+++ src/tests/testPrecession.cpp	2015-07-28 19:18:20 +0000
@@ -0,0 +1,121 @@
+/*
+ * Stellarium 
+ * Copyright (C) 2015 Georg Zotti
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335, USA.
+ */
+
+#include <QObject>
+#include <QtDebug>
+#include <QVariantList>
+#include <QtTest>
+
+#include "tests/testPrecession.hpp"
+#include "StelUtils.hpp"
+#include "VecMath.hpp"
+
+QTEST_MAIN(TestPrecession)
+
+static const double arcSec2Rad=M_PI*2.0/(360.0*3600.0);
+static const double eps0=84381.406*arcSec2Rad;
+
+void TestPrecession::initTestCase()
+{
+}
+
+// example data found in Vondrak et al. 2011: New Precession Expressions, Valid for Long Time Intervals. A&A534, A22.
+// Section A.5
+// pecl = ( +0.00041724785764001342 -0.40495491104576162693 +0.91433656053126552350 )
+//      = ( P_A                     -Q_A*C-Z*S              -Q_A*S+Z*C              )
+// pequ = ( -0.29437643797369031532 -0.11719098023370257855 +0.94847708824082091796 )
+//      = ( X                        Y                       sqrt(1-x^2-y^2) || 0   )
+// This provides only the axes formulation. But the final Precession matrix should then be used as reference
+// comparable to the matrix that can be reached via the Capitaine parametrisation that we are using.
+
+void TestPrecession::testPrecessionAnglesVondrak()
+{
+	const double S=sin(eps0);
+	const double C=cos(eps0);
+	double Z, W;
+	double JulianDay=1219339.078000; // TT
+	double epsilon_A, chi_A, omega_A, psi_A;
+	double P_A, Q_A, X_A, Y_A;
+	double VEC2, VEC3, VEQ3;
+
+	// get angles for Capitaine parameterisation
+	getPrecessionAnglesVondrak(JulianDay, &epsilon_A, &chi_A, &omega_A, &psi_A);
+	// Get reference angles. We have to call this twice with different dates to avoid returning the cached (zero) angles.
+	getPrecessionAnglesVondrakPQXYe(-1234.567, &P_A, &Q_A, &X_A, &Y_A, &epsilon_A);
+	getPrecessionAnglesVondrakPQXYe(JulianDay, &P_A, &Q_A, &X_A, &Y_A, &epsilon_A);
+	Z=sqrt(qMax(1.0-P_A*P_A-Q_A*Q_A, 0.0));
+	W=X_A*X_A+Y_A*Y_A;
+	VEC2=-Q_A*C -Z*S;
+	VEC3=-Q_A*S +Z*C;
+	VEQ3=(W<1.0 ? sqrt(1.0-W) : 0.0);
+
+	QVERIFY2(fabs(P_A -0.00041724785764001342)<=0.000001, QString("JD %1: Pecl,x: %2 Difference: %3").arg(JulianDay).arg(P_A ).arg(P_A -0.00041724785764001342).toUtf8());
+	QVERIFY2(fabs(VEC2+0.40495491104576162693)<=0.000001, QString("JD %1: Pecl,y: %2 Difference: %3").arg(JulianDay).arg(VEC2).arg(VEC2+0.40495491104576162693).toUtf8());
+	QVERIFY2(fabs(VEC3-0.91433656053126552350)<=0.000001, QString("JD %1: Pecl,z: %2 Difference: %3").arg(JulianDay).arg(VEC3).arg(VEC3-0.91433656053126552350).toUtf8());
+	QVERIFY2(fabs(X_A +0.29437643797369031532)<=0.000001, QString("JD %1: Pequ,x: %2 Difference: %3").arg(JulianDay).arg(X_A ).arg(X_A +0.29437643797369031532).toUtf8());
+	QVERIFY2(fabs(Y_A +0.11719098023370257855)<=0.000001, QString("JD %1: Pequ,y: %2 Difference: %3").arg(JulianDay).arg(Y_A ).arg(Y_A +0.11719098023370257855).toUtf8());
+	QVERIFY2(fabs(VEQ3-0.94847708824082091796)<=0.000001, QString("JD %1: Pequ,z: %2 Difference: %3").arg(JulianDay).arg(VEQ3).arg(VEQ3-0.94847708824082091796).toUtf8());
+	// the same, to be seen ...
+//	qDebug() << QString("JD %1: Pecl,x: %2 Difference: %3").arg(JulianDay, 8, 'f', 5).arg(P_A , 15, 'f', 12).arg(P_A -0.00041724785764001342, 15, 'f', 12);
+//	qDebug() << QString("JD %1: Pecl,y: %2 Difference: %3").arg(JulianDay, 8, 'f', 5).arg(VEC2, 15, 'f', 12).arg(VEC2+0.40495491104576162693, 15, 'f', 12);
+//	qDebug() << QString("JD %1: Pecl,z: %2 Difference: %3").arg(JulianDay, 8, 'f', 5).arg(VEC3, 15, 'f', 12).arg(VEC3-0.91433656053126552350, 15, 'f', 12);
+//	qDebug() << QString("JD %1: Pequ,x: %2 Difference: %3").arg(JulianDay, 8, 'f', 5).arg(X_A , 15, 'f', 12).arg(X_A +0.29437643797369031532, 15, 'f', 12);
+//	qDebug() << QString("JD %1: Pequ,y: %2 Difference: %3").arg(JulianDay, 8, 'f', 5).arg(Y_A , 15, 'f', 12).arg(Y_A +0.11719098023370257855, 15, 'f', 12);
+//	qDebug() << QString("JD %1: Pequ,z: %2 Difference: %3").arg(JulianDay, 8, 'f', 5).arg(VEQ3, 15, 'f', 12).arg(VEQ3-0.94847708824082091796, 15, 'f', 12);
+
+
+	Vec3d PECL(P_A, VEC2, VEC3);
+	Vec3d PEQR(X_A, Y_A, VEQ3);
+	Vec3d EQX=PEQR^PECL;
+	EQX.normalize();
+	Vec3d V=PEQR^EQX;
+	Mat3d RP(EQX[0], EQX[1], EQX[2], V[0], V[1], V[2], PEQR[0], PEQR[1], PEQR[2]); // result from paper, section A.3
+	// Now we create the (hopefully) same rotation matrix from the Capitaine angles.
+	// Mat4d Rrot=Mat4d::zrotation(chi_A) * Mat4d::xrotation(-omega_A) * Mat4d::zrotation(-psi_A) * Mat4d::xrotation(eps0);
+
+	// Uh-oh - it seems the A&A paper has the matrix operations in the other direction.
+	// So the matrix to be compared must be composed in reverse.
+	Mat4d RRot=Mat4d::xrotation(eps0)*Mat4d::zrotation(-psi_A) * Mat4d::xrotation(-omega_A) * Mat4d::zrotation(chi_A);
+
+	//qDebug() << "RP     : " << RP.toString(15, 'f', 12);
+	//qDebug() << "RcapTr : " << RRot.upper3x3().toString(15, 'f', 12);
+
+	Mat4d RP4(EQX[0], EQX[1], EQX[2], 0, V[0], V[1], V[2], 0, PEQR[0], PEQR[1], PEQR[2], 0, 0, 0, 0, 1);
+	//QMatrix4x4 matDiff=((RRot-RP4)).convertToQMatrix();
+	//qDebug() << matDiff;
+	Mat3d matDiff3x3=(RRot-RP4).upper3x3();
+	double max=0.0;
+	for (int i=0; i<9; ++i)
+	{
+		if (fabs(matDiff3x3[i]) > max)
+			max=fabs(matDiff3x3[i]);
+	}
+	//qDebug() << "largest value in difference of matrices:" << max;
+	QVERIFY2(max<2e-5, QString("Some values in the precession matrices differ by too much.").toUtf8());
+
+	double angleRef=RP.angle()*180.0/M_PI;
+	double angleCap=RRot.upper3x3().angle()*180.0/M_PI;
+	//qDebug() << "Rotation angle of reference matrix:" << angleRef;
+	//qDebug() << "Rotation angle of Capitaine matrix:" << angleCap;
+	//qDebug() << "Difference (arcseconds):" << (angleCap-angleRef)*3600.0;
+	// according to Fig12 in the paper, a few arcseconds of difference between PQXY and Capitaine parametrisation are allowed.
+	QVERIFY2((angleCap-angleRef)*3600.0<6.0, QString("Angle between rotation matrices too different!").toUtf8());
+
+	//TODO: Add more dates and verify this angle difference is limited to what we can see in Fig.12
+}

=== added file 'src/tests/testPrecession.hpp'
--- src/tests/testPrecession.hpp	1970-01-01 00:00:00 +0000
+++ src/tests/testPrecession.hpp	2015-07-28 19:18:20 +0000
@@ -0,0 +1,35 @@
+/*
+ * Stellarium
+ * Copyright (C) 2015 Georg Zotti
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335, USA.
+ */
+
+#ifndef _TESTPRECESSION_HPP_
+#define _TESTPRECESSION_HPP_
+
+#include <QObject>
+#include <QtTest>
+#include "precession.h"
+
+class TestPrecession : public QObject
+{
+	Q_OBJECT
+private slots:
+	void initTestCase();	
+	void testPrecessionAnglesVondrak(); 
+};
+
+#endif // _TESTPRECESSION_HPP_