<p>I want to use the SPICE software, but there is something than I don't understand:</p>
<blockquote>
<p>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.</p>
</blockquote>
<p>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?</p>

CC BY-SA 4.0
2024-03-17T21:35:43.900Z
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
CC BY-SA 4.0
2024-03-18T07:43:24.123Z
https://en.wikipedia.org/wiki/Ephemeris
planetmaker
CC BY-SA 4.0
2024-03-18T08:01:16.203Z
@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
CC BY-SA 4.0
2024-03-18T10:30:03.093Z
If you intend to use SPICE you should probably look at the tutorials.   https://naif.jpl.nasa.gov/naif/tutorials.html
PM 2Ring
CC BY-SA 4.0
2024-03-18T10:33:40.523Z
@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
CC BY-SA 4.0
2024-03-18T10:35:55.353Z
I'm using MaxQ with Unreal Engine. But I want to understand everything about SPICE because I'm curious. Thank you.
VansFannel
CC BY-SA 4.0
2024-03-18T10:37:28.560Z
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
CC BY-SA 4.0
2024-03-18T10:50:18.957Z
@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
CC BY-SA 4.0
2024-03-18T16:11:14.903Z
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
<ephemeris>
What are ephemerides? (SPICE software)
VansFannel
# What are ephemerides? (SPICE software)

(Asked by: username_0 on 2024-03-17)

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?

**Tags:** ephemeris

> **Comments:**
> **username_1**: 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/  
> **username_2**: https://en.wikipedia.org/wiki/Ephemeris  
> **username_0**: @username_2 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.  
> **username_3**: If you intend to use SPICE you should probably look at the tutorials.   https://naif.jpl.nasa.gov/naif/tutorials.html  
> **username_0**: @username_3 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.  
> **username_0**: I'm using MaxQ with Unreal Engine. But I want to understand everything about SPICE because I'm curious. Thank you.  
> **username_3**: 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.  
> **username_0**: @username_3 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.  
> **username_1**: 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  

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## 0 answers

