Stellarium

Slight differences in Moon ephemeris (of a few minutes)

Asked by Ivan Marti-Vidal

Dear all,

I'm happy to tell you that the "Observability" plugin is finally ready!!!!

The code is in:

lp:~i-martividal/stellarium/Observability

So if you could take a look to it, I would be very thankful for your feedback! Indeed, I don't know how to proceed from now on. Should I propose the code for merging, or wait for some testing from you all?

However, as I told in an earlier e-mail, something weird happens to the Moon when I try to get the ephemeris. The differences between the renderized Moon and my estimates of rise/set times are of a few minutes (about 3-4 minutes). This is the code for getting the Moon's ephemeris ("myEarth" points to the Earth and "myMoon" points to the Moon :D):

   myEarth->computePosition(jd1);
   myEarth->computeTransMatrix(jd1);
   Pos0 = myEarth->getHeliocentricEclipticPos();
   LocTrans = (core->matVsop87ToJ2000)*(Mat4d::translation(-Pos0));
   myMoon->computePosition(jd1);
   myMoon->computeTransMatrix(jd1);
   Pos1 = myMoon->getHeliocentricEclipticPos();
   Pos2 = core->j2000ToEquinoxEqu(LocTrans*Pos1);

I assume that "Pos2" should be the position of the Moon at the date jd1, in the instantaneous equatorial frame of the Earth. Am I right? However, I've printed the position and compared to that shown in the screen, and they differ by a few minutes! I'm a bit messed with this!

     Best Wishes,

                Ivan

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Revision history for this message
Alexander Wolf (alexwolf) said : 		#1

I play with your plugin. It's nice, but you need make few improvements:
1. Add GUI for access to configurable settings.
2. Into getPluginInfo() you need change q_() on N_()
3. You need update "layer" for info box, because landscapes hide current info

Revision history for this message
Worachate Boonplod (worachateb) said : 		#2

Is this something to do with parallax and/or atmospheric refraction?
They're important factors when computing rise/set time of celestial objects.

Revision history for this message
gzotti (georg-zotti) said : 		#3

Indeed, parallax and refraction both influence rising/setting times for the moon.
Regards, G.

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