# I JPL ephemeris files

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1. Dec 30, 2017

### cptolemy

Greetings,

This is actually a simple question. I'm working on the JPL ephemeris original data. My question is: If I wish to calculate the heliocentric position of, let's say, Mars from the original JPL raw data, must I calculate first the x,y and z position (an easy process) and then subtract the 11th value - the Sun - to these coordinates?
The JPL frame is refered to the SS barycenter, right? So I must subtract these values I presume.

Kind regards,

CPtolemy

2. Jan 1, 2018

### Baluncore

Exactly which original data would that be? Do you have a link? Horizons?
If the coordinate system is referenced to the barycentre, then the Sun will have coordinates that are small, close to, but not equal to zero.
So if that is the case, yes, subtract the Sun's coordinates from the object's coordinates to get the object's heliocentric position.