I have zero clue in astronomy and I need astronomical data to write a program. What I learned so far:
- celestial coordinates are usually measured relatively to vernal equinox aka meridian of First point of Aries (which is not located in Aries anymore)
- the GHA of first point of Aries changes constantly
I was searching for vernal equinox GHA data and it seems to me that this personal, generated Almanac version lists it as "Aries" (it was misleading me).
I expected that
( GHA(object) - GHA(v. equinox) ) mod 24h = RA (object)
as per this article. However I have found a program which calculates declination and right ascension and I have found out that the relation is sort of inverse. For example:
And the program output:
JD 2458849.50, 2019 December 31 Tuesday 23h 58m 49.174s UT 2020
January 1 Wednesday 0h 00m 00.000s TDT nutation dRA -1.043s dDec
-6.12" Geometric lon -13.866 deg, lat -4.894 deg, rad 2.6996e-003 au Apparent geocentric longitude 346.129 deg latitude -4.894 deg
Distance 63.319 Earth-radii Horizontal parallax 0d 54' 17.67"
Semidiameter 0d 14' 47.60" Elongation from sun 66.20 deg,
Illuminated fraction 0.30 Phase 2.0 days before First Quarter
Apparent: R.A. 23h 16m 38.283s Declination - 9d 58' 41.62"
Local apparent sidereal time 1h 54m 46.005s diurnal aberration dRA
0.012s dDec -0.03" diurnal parallax dRA -104.977s dDec -2485.74" atmospheric refraction 0.033 deg dRA 4.296s dDec 102.06" Topocentric:
Altitude 25.678 deg, Azimuth 224.447 deg Topocentric: R.A. 23h 14m
57.615s Dec. - 10d 38' 25.32" local meridian transit 2019 December 31 Tuesday 21h 16m 02.396s UT rises 2019 December 31 Tuesday 15h 49m
26.475s UT sets 2020 January 1 Wednesday 2h 50m 11.075s UT Visible hours 11.0124
110 deg 56,9 sec - 100 deg 7,1 sec = 10 deg 49,8 sec
which is inverse of R.A. which program lists.
Do I have a misconception?