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I want to use the SPICE software, but there is something than I don't understand:

The purpose of the SPK---which stands for S(pacecraft) and P(lanet) Kernel---file is to allow ephemerides for any collection of solar system bodies to be combined under a common file format, and accessed by a common set of functions.

What are ephemerides here? Are they a table with all of the positions of a celestial body in a period of time? Do I have to use the SPK to find out where a planet is at any given time?

VansFannel
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  • Ephemerides is the term used for the data used to compute the position of an object. So, yes, you need the correct SPK to generate positions for an object. You can get them from here: https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/ – Greg Miller Mar 17 '24 at 21:35
  • https://en.wikipedia.org/wiki/Ephemeris – planetmaker Mar 18 '24 at 07:43
  • @planetmaker Thank you. That was the first I checked, but I don't understand it in the context of SPICE software. By the way, I have updated my question with more details about what I don't understand. – VansFannel Mar 18 '24 at 08:01
  • If you intend to use SPICE you should probably look at the tutorials. https://naif.jpl.nasa.gov/naif/tutorials.html – PM 2Ring Mar 18 '24 at 10:30
  • @PM2Ring Do the tutorials explain the meaning of ephemerides? Because this is the only problem I have. I don't understand the meaning of ephemerides in this context. Thank you. – VansFannel Mar 18 '24 at 10:33
  • I'm using MaxQ with Unreal Engine. But I want to understand everything about SPICE because I'm curious. Thank you. – VansFannel Mar 18 '24 at 10:35
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    The SPK files encode position data as a series of polynomials, with each polynomial covering a short timespan. Using a given polynomial, you can calculate accurate position & velocity data for a body, for any time within that timespan. – PM 2Ring Mar 18 '24 at 10:37
  • @PM2Ring MaxQ is wrapped of SPICE C library. It enables to use it with Unreal. I'm developing a VR astronomical software and I want it as accurate as possible. – VansFannel Mar 18 '24 at 10:50
  • This article explains how the data in the SPK files are used to compute the position. The article is about the JPL DE files, but the SPK files have the exact same data, just in a different format. https://celestialprogramming.com/jpl-ephemeris-format/jpl-ephemeris-format.html – Greg Miller Mar 18 '24 at 16:11

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