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I'm working on an animation that replicates our Solar System. I know this has been done before, but I'm working on something that requires me to make one myself. With that being said, I'm having a tough time deciphering the JPL Ephemerides. Particularly for the Moon because I have already figured out how to work the VSOP Ephemerides, which gives me the positions for the planets.

Does anyone know of a source I could use to learn how to utilize the ASCII JPL Epehemerides file that are found here? It would be a huge help and I think a step by step walk through would probably help others in the future.

Thanks!

Link to Epheremerides files

Jee
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2 Answers2

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There is a python package called Skyfield that loads, reads and interpolates the binary forms of the JPL Development Ephemerides or DEs for you, and does everything else you need to get the absolute best results possible from them. If you can use even a tiny bit of python then this would be the way to go rather than trying to figure out how to interpolate JPL's "special flavor" of Chebyshev polynomials.

See these in Space Exploration SE:

and also see how easy it is to do things like this with Skyfield in this answer to Sunset on [Mountain] from [Viewing Point]

Also this answer to How to calculate the planets and moons beyond Newtons's gravitational force? shows how I used JPL's Horizons interface output (which also interpolates the DEs using Spice) to compare my numerical orbit integrator results to the ephemerides.

And just for fun see How to pronounce “Ephemerides”? in English SE.

uhoh
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  • Is your bounty trying to say that Huy Pham is correct and deserves to be marked as the answer? – Jee Jun 12 '20 at 17:45
  • Looking for an answer here. I haven't been able to completely verify either answer because I have not had time to do so. So in order to avoid wasting your bounty, I would love to hear your input for which answer you are referring to. – Jee Jun 13 '20 at 23:02
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    @whathm Sorry, for some reason I missed your first comment. No, the bounty is totally independent of what you would like to choose to accept if you decide to accept anything at all. It's just for a new user who found a really interesting/useful link. – uhoh Jun 13 '20 at 23:12
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    @whathm as an aside, the Python package Skyfield is a complete solution, if you are pressed for time and it does what you need, it's an excellent solution. – uhoh Jun 13 '20 at 23:14
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    Ahh gotcha. I think I misunderstood how bounties work. You can assign it to any answer regardless of whether the question asker has chosen a solution. Is that correct? – Jee Jun 13 '20 at 23:15
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    Aaaand you just assigned it. Hahaha ok, I totally misunderstood them. Sorry about that. – Jee Jun 13 '20 at 23:16
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    @whathm no reason to be sorry at all! Comments are for clarification, and Stack Exchange is different than most other sites and takes a while getting used to. – uhoh Jun 13 '20 at 23:17
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    Understood, thanks! And as for Skyfield. I took a quick look at it and it looks like it'll be super helpful. I'll get back to you as soon as I get around to digging deeper into it. Thanks again! – Jee Jun 13 '20 at 23:18
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This link even gives you the algorithm to calculate: link here

Also, if you are comfortable with the VSOP, the VSOP2000 does have the moon data... the ephemerides can be downloaded from here

Huy Pham
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