# Does Celestia respect 'setframe' coordinate systems?

Through trial and error (see script below that summarizes what I've found), I've learned Celestia's coordinate system appears to be:

• The x axis points to the vernal equinox

• The y axis points to the ecliptic north pole

• The z axis points to 18 hours right ascension, -23.4393 declination (ie, the obliquity of the ecliptic)

regardless of whether you choose the "equatorial", "ecliptical", or "universal" frames.

I wrote the script below to confirm this: regardless of which setframe command you uncomment (or if you leave them all commented), the results are the same.



{

# using Celestia 1.6.1

# set to equatorial frame
# setframe {ref "Sol/Earth" coordsys "equatorial"}
# setframe {ref "Sol/Earth" coordsys "ecliptical"}
# setframe {ref "Sol/Earth" coordsys "universal"}

# 27 Psc is near the vernal equinox at a distance of 234.48 ly
# this brings me within 14 ly
setposition {base [234.48 0 0]}
select {object "27 Psc"}
center {time 0.01}
wait {duration 3.0}

# 42 Dra is near the north ecliptic pole at 18h, 66.56 declination
# this brings me within 15 ly
setposition {base [0 314.82 0]}
select {object "42 Dra"}
center {time 0.01}
wait {duration 3.0}

# 7 Sgr is near the 18h, -23.4393 declination
# this brings me within 20 ly
setposition {base [0 0 1079.99]}
select {object "7 Sgr"}
center {time 0.01}
wait {duration 3.0}

}



I am aware that https://en.wikibooks.org/wiki/Celestia/Binary_Star_File suggests the coordinates are stored internally as some gyration of ecliptical coordinates, but assumed "setframe" would change this.

• I'm voting to close this question as off-topic because it seems like a question suitable for e.g. the Celestia forum rather than Astronomy SE. – StephenG Sep 16 '18 at 13:38
• Maybe setposition always operates in "universal" coordinates. What effect does setframe have on other movement commands? – Mike G Sep 16 '18 at 13:42
• @StephenG I went ahead and added it there, but I think it's appropriate here too. There are plenty of questions about stellarium here, and I think it's reasonable to discuss popular astronomy software here, just as it's reasonable to discuss qgis, grass, and other GIS software on gis.SE – barrycarter Sep 16 '18 at 16:42
• My message was rejected on the Celestia Forums: ": The reported message has the only purpose to advertise for a website or another product..". I guess there ARE sites with worse moderators! – barrycarter Sep 17 '18 at 18:34