Barycentric or Heliocentric?

[fraserw]

It isn't clear from the TOMs interface if the elements required of a custom moving object are in heliocentric, barycentric, or some other coordinate system with less common origin. The JPL queries and MPC queries imply heliocentric coordinates. I have two feature requests:

1) Clarify this in the top text of the target creation and information pages.

2) Provide a converter between the barycentric and heliocentric elements to enable input of both types.

Think of it as the metric vs. imperial battle...

[dmcollom]

Wes, very happy to add labels explicitly saying that everything is stored in heliocentric (which it obviously is, given that the two data sources you mentioned return them in said format.

A converter is definitely an option, provided there's a relatively straightforward way of doing so. We do something very similar with sexagesimal targets here, but it's not immediately clear (to me, at least) how I would implement the conversion. It doesn't appear that Astropy provides it either. Do you have a resource on that?

[fraserw]

Unfortunately it isn't so simple as it requires at least two steps of an integrator at the epoch of the elements. But I can do this using rebound, which is python friendly. I'll look at adding this during my other ephemeris-centric development.

On Fri., Jan. 31, 2020, 3:19 p.m. David Collom notifications@github.com wrote:

Wes, very happy to add labels explicitly saying that everything is stored in heliocentric (which it obviously is, given that the two data sources you mentioned return them in said format.

A converter is definitely an option, provided there's a relatively straightforward way of doing so. We do something very similar with sexagesimal targets here https://github.com/TOMToolkit/tom_base/blob/master/tom_targets/templatetags/targets_extras.py#L140, but it's not immediately clear (to me, at least) how I would implement the conversion. It doesn't appear that Astropy provides it either. Do you have a resource on that?

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