<p>I am using the <a href="https://ssd.jpl.nasa.gov/horizons/" rel="nofollow noreferrer">JPL horizons app</a> to generate an SPK file for Chiron (ID: 20002060) with respect to the solar system barycenter (ID: 0). However, the generated SPK file says the center is with respect to the sun (ID: 10). What is happening and what is the correct center? I'm assuming the correct center is probably 10, but why is Horizons generating an ephemeris file with a different center than specified on the webapp?</p>
<h1>The Horizons Input</h1>
<p><a href="https://i.sstatic.net/4V4bj.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4V4bj.png" alt="enter image description here" /></a></p>
<h1>The Generated Ephemeris</h1>
<p>This is the text after decoding the binary data.</p>
<p><a href="https://i.sstatic.net/RASZS.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/RASZS.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2024-02-29T14:25:33.450Z
Note that the `Coordinate Center` button is ghosted, so you don't actually have a choice. Here's the SPICE Tutorials page: https://naif.jpl.nasa.gov/naif/tutorials.html 18_spk may be helpful.
PM 2Ring
CC BY-SA 4.0
2024-02-29T14:39:13.600Z
What do you want to do with this SPK file? Are you using it with the SPICE Toolkit?
PM 2Ring
CC BY-SA 4.0
2024-02-29T20:38:48.643Z
@PM2Ring I was aware that the button is ghosted but I assumed the filled in value of SSB was the center of the SPK file. Maybe it's not and it's just a placeholder with no relation to the file. I ultimately found a workaround, but I am using it in a python script. I read the file in using the `spktype21` python library, and then integrate the kernel object with `skyfield`, but `skyfield` requires the data to be relative to the solar system's barycenter, so I just did some vector addition to make the correction
Hunter
<observational-astronomy><horizon>
Horizons SPK file with a different coordinate center than I asked for
Hunter
# Horizons SPK file with a different coordinate center than I asked for

(Asked by: username_0 on 2024-02-29)

I am using the [JPL horizons app](https://ssd.jpl.nasa.gov/horizons/) to generate an SPK file for Chiron (ID: 20002060) with respect to the solar system barycenter (ID: 0). However, the generated SPK file says the center is with respect to the sun (ID: 10). What is happening and what is the correct center? I'm assuming the correct center is probably 10, but why is Horizons generating an ephemeris file with a different center than specified on the webapp?

# The Horizons Input

[![enter image description here](https://i.sstatic.net/4V4bj.png)](https://i.sstatic.net/4V4bj.png)

# The Generated Ephemeris

This is the text after decoding the binary data.

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

**Tags:** observational-astronomy, horizon

> **Comments:**
> **username_1**: Note that the `Coordinate Center` button is ghosted, so you don't actually have a choice. Here's the SPICE Tutorials page: https://naif.jpl.nasa.gov/naif/tutorials.html 18_spk may be helpful.  
> **username_1**: What do you want to do with this SPK file? Are you using it with the SPICE Toolkit?  
> **username_0**: @PM2Ring I was aware that the button is ghosted but I assumed the filled in value of SSB was the center of the SPK file. Maybe it's not and it's just a placeholder with no relation to the file. I ultimately found a workaround, but I am using it in a python script. I read the file in using the `spktype21` python library, and then integrate the kernel object with `skyfield`, but `skyfield` requires the data to be relative to the solar system's barycenter, so I just did some vector addition to make the correction  

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## 0 answers

