RA/Dec confusion

[Evil Dr Ganymede]

While fiddling around with my Antares system, I realised that I'd put Antares in the wrong place in the sky (somehow, it ended up a few degrees away from to Betelgeuse!)

It's a bit of a fudge, but the way I'm doing this is to make a new stc file, call it hip500000.stc or something, and then put the 'corrected' Antares star data into that. Then when Celestia loads up, the new Antares replaces the old one. (actually, the old one's still there, it's just that Celestia doesn't think it's the real one when you type it in as a target to go to. Like I said, it's a fudge).

However, if I put in the correct values for Antares from the Hipparcos star catalogue into the stc file, (see http://astro.estec.esa.nl/Hipparcos/HIP ... earch.html , look for HIP 80763), it lands up not being in Scorpio.

I don't know where I'm going wrong here. According to the Hipparcos data, the RA and dec should be:

RA: 16 29 24.47 (hms, J1991.25)
Dec: -26 25 55.0 (dms, J1991.25)

To convert that to decimal values used in Celestia, I presume I just have to enter those into the sexagesimal mode on my calculator ( the [° ' "] button), and then convert that to decimals, so I get:

RA: 16.49
Dec: -26.432

But if I enter that into the stc file, my 'fake Antares' doesn't end up where it should be - in fact, it lands up in the constellation of Sculptor.

Am I doing something wrong in the calculation here? Either way, can someone tell me the correct RA and Dec to put into the stc file so the fake Antares appears in the same place as the real one?

Here's the stc file...

#######################
#hip500000.stc (fake antares)
#######################
# HIP 80763
80763 {
RA 16.49
Dec -26.432
Distance 604.014
SpectralType "M5Ia-b"
AppMag -1.5
}
#######################

[selden]

Dr. Ganymede,

That's because the RA value used by .STC files is measured in degrees, not hours.
Just to add to the confusion, the RA value used by .DSC files is measured in hours.

It seems that many astronomical databases provide RA in degrees, which started the confusion. I've suggested that textual alternatives be provided (as are available for the Epoch values in .SSC files), but it doesn't look like that option will happen soon.

[Evil Dr Ganymede]

So to convert from hms to dms, what do you do? I'm figuring divide the hms value by 24, then multiply that by 360 - does that sound right?

So the correct RA for Antares should be 247.352 ?

That looks about right. Only problem is that it's not quite in the same place as the real Antares, so now I've got two Antares there... And annoyingly enough, it won't let me not use the stars.dat file, the program won't start if it doesn't have a stars.dat file to load up

Oh well. At least I know how to do it now