# Planets orbit fitting

I would like to fit planets orbits. To do this, I need a set of mock observations. I can get them from right ascension/declination obtained from the Horizons interface: EDIT: Horizons gives me a list {time,right ascension [hms],declination[dms]}. I need to reconstruct at least one observed orbit, for example of Mercury, around the Sun. My confusions is: how to convert the output coordinates from Horizons? Is it sufficient to convert them from equatorial to ecliptic?

Is there any suggestion to implement the correct procedure?

EDIT 2:

I changed the settings in Horizons in this way To have {X,Y,Z} in AU and the Sun as body center. Then I tried to overlap simulated orbit with Newton's equation with the horizons coordinates. Is this the right way to make the coordinates comparable for a fit?

• What exactly is your question? Orbit fitting from three observations is a complex calculation, and least squares analysis to fit from more than three adds another layer. Are you asking how to fit an orbit to observations? Or are you asking how to get an list of "mock" observations from Horizons.? Apr 23, 2021 at 19:25
• I'm asking how to obtain a list of mock observations from Horizons. Apr 23, 2021 at 20:55
• I guess right ascension and declination are referred to ICRF. I would use a similar procedure: 1) convert equatorial to ecliptic coordinates. 2) add gaussian deviations to the true positions. But I don't know If I'm on the right way. Apr 23, 2021 at 21:07
• You can search the internet, here in Astronomy SE or in Space Exploration SE for many examples; it's a big topic. Why not do a little reading and then elaborate more on what exactly you'd like to do? There's one nice method described in the paper linked in this comment, is that along the lines of what you want to do?
– uhoh
Apr 24, 2021 at 2:12
• I tried to be more specific! I need to understand properly how to treat the output coordinates from Horizons before fitting . Apr 24, 2021 at 8:36