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skyfielders / python-skyfield

Elegant astronomy for Python
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How to get the same coords as in JPL Horizons from mpcorb.dat orbits? #649

Closed xmichaelx closed 2 years ago

xmichaelx commented 2 years ago

Object: (285571) 2000 PQ9 Time: 2021-08-14T23:48:00Z Location (lat,lon,alt): 28.2999988, -16.50583131, 2500

JPL/Horizons gives topocentric astrometric ICRF coords: 317.08673, 40.74741 Using (earth+observatory).at(t).observe(sun + object).radec() gives: 317.06759, 40.71264 About -68.9, -125.2 arcsec of difference in RA and DEC respectably. How can I do better in skyfield?

Gist to code: https://gist.github.com/xmichaelx/4764f761168cfb365e242c08d0adb2e7

xmichaelx commented 2 years ago

In the meantime I've checked how OpenOrb is doing on that particular data and got something around: 317.06744, 40.71232 which is pretty close to what skyfield returns.

Question for more experienced people - should I expect that results based on mpcorb.dat will be less precise than export from JPL Horizons? JPL Horizons correlation is near pixel-perfect on my observations.

xmichaelx commented 2 years ago

This was an issue with using propagator not taking into account perturbations for orbits more than 40 days old.