Right ascension / Declination of a satellite

Question

I work whit Heavensat program to understand the behavior of satellites around the Earth, lately something surprised me. The question is that "Are Right ascension / Declination values of a satellite invariant for different observer on the earth at a fixed time?"

I thought that the answer is "Yes", But in this program when I change the observer location, the values of RA/dec will change!

I used some other algorithm to calculate RA/dec manually and check the program. The output was the same!

These are the output of heavensat for a fixed satellite and time for two different observer site:

I changed the observer site a little and you can see the changes in RA/dec

Is there anything I should know about Right ascension and Declination? Or it has different concept for satellites?

Thanks

Answer 1

RA and DEC indicate the position of the satellite on the background sky. Star positions can be described with RA/DEC because they are infinitely far and do not move relatively to one another when you change your position. Satellites are much closer, so if you move they will move compared to the star background.

This is why if you change observer site you will see the satellite RA and DEC will change.

They do not define the satellite position but the direction toward the satellite.