Undergrad JPL Ephemeris Files: Calculating Heliocentric Pos. of Mars

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To calculate the heliocentric position of Mars using JPL ephemeris data, one must first determine the x, y, and z coordinates of Mars. The coordinates are referenced to the Solar System barycenter, meaning the Sun's coordinates will be close to zero but not exactly. Therefore, to find Mars' heliocentric position, subtract the Sun's coordinates from Mars' coordinates. The discussion emphasizes the importance of understanding the reference frame when performing these calculations. Accurate calculations rely on using the correct original data from JPL, such as the Horizons system.
cptolemy
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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 referred to the SS barycenter, right? So I must subtract these values I presume.

Kind regards,

CPtolemy
 
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cptolemy said:
I'm working on the JPL ephemeris original data
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.
 
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