<p>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:</p>
<p><a href="https://i.sstatic.net/01npr.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/01npr.png" alt="enter image description here" /></a></p>
<p>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?</p>
<p>Is there any suggestion to implement the correct procedure?</p>
<p>EDIT 2:</p>
<p>I changed the settings in Horizons in this way
<a href="https://i.sstatic.net/01npr.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/01npr.png" alt="enter image description here" /></a></p>
<p>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. <a href="https://i.sstatic.net/sMLYc.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/sMLYc.jpg" alt="enter image description here" /></a></p>
<p>Is this the right way to make the coordinates comparable for a fit?</p>

CC BY-SA 4.0
2021-04-23T19:25:01.660Z
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.?
James K
CC BY-SA 4.0
2021-04-23T20:55:26.753Z
I'm asking how to obtain a list of mock observations from Horizons.
Orion
CC BY-SA 4.0
2021-04-23T21:07:56.273Z
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.
Orion
CC BY-SA 4.0
2021-04-24T02:12:42.350Z
You can search the internet, here in Astronomy SE or in [Space Exploration SE](https://space.stackexchange.com/) 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](https://astronomy.stackexchange.com/questions/43382/keplerian-elements#comment88574_43382), is that along the lines of what you want to do?
uhoh
CC BY-SA 4.0
2021-04-24T08:36:25.527Z
I tried to be more specific! I need to understand properly how to treat the output coordinates from Horizons before fitting .
Orion
CC BY-SA 4.0
2021-04-24T13:37:20.867Z
Thanks for the edit! For a general tutorial about Horizons see [this answer](https://space.stackexchange.com/a/25357/12102) in Space Exploration SE, and to get altitude/azimuth observations from a given latitude/longitude on a major celestial body (Earth or otherwise) see [this answer](https://space.stackexchange.com/a/37155/12102). If you use Python a little bit or would like to learn then have a look at [Skyfield](https://rhodesmill.org/skyfield/) There are many Q&A and helpful scripts here and in Space SE if you search for Skyfield; uses same/similar ephemerides as Horizons but runs locally
uhoh
CC BY-SA 4.0
2021-04-24T15:40:28.753Z
But Horizons does it all for you. Just select 'Orbital Elements' for the Ephemeris Type.
Thomas
CC BY-SA 4.0
2021-04-26T07:22:13.790Z
Thank you all I will study a tutorial for Horizons!
Orion
<orbit><ephemeris>
Planets orbit fitting
Orion
# Planets orbit fitting

(Asked by: username_0 on 2021-04-23)

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:

[![enter image description here](https://i.sstatic.net/01npr.png)](https://i.sstatic.net/01npr.png)

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
[![enter image description here](https://i.sstatic.net/01npr.png)](https://i.sstatic.net/01npr.png)

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. [![enter image description here](https://i.sstatic.net/sMLYc.jpg)](https://i.sstatic.net/sMLYc.jpg)

Is this the right way to make the coordinates comparable for a fit?

**Tags:** orbit, ephemeris
> **Comments:**
> **username_1**: 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.?  
> **username_0**: I'm asking how to obtain a list of mock observations from Horizons.  
> **username_0**: 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.  
> **username_2**: You can search the internet, here in Astronomy SE or in [Space Exploration SE](https://space.stackexchange.com/) 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](https://astronomy.stackexchange.com/questions/43382/keplerian-elements#comment88574_43382), is that along the lines of what you want to do?  
> **username_0**: I tried to be more specific! I need to understand properly how to treat the output coordinates from Horizons before fitting .  
> **username_2**: Thanks for the edit! For a general tutorial about Horizons see [this answer](https://space.stackexchange.com/a/25357/12102) in Space Exploration SE, and to get altitude/azimuth observations from a given latitude/longitude on a major celestial body (Earth or otherwise) see [this answer](https://space.stackexchange.com/a/37155/12102). If you use Python a little bit or would like to learn then have a look at [Skyfield](https://rhodesmill.org/skyfield/) There are many Q&A and helpful scripts here and in Space SE if you search for Skyfield; uses same/similar ephemerides as Horizons but runs locally  
> **username_3**: But Horizons does it all for you. Just select 'Orbital Elements' for the Ephemeris Type.  
> **username_0**: Thank you all I will study a tutorial for Horizons!  

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## 0 answers

