[AstroPy] What should I know in advance to understand get_body(planet, time, location)?
Yang Hon-Jang
hjyanghj at gmail.com
Fri Dec 22 19:37:16 EST 2017
As far as I know get_body('mars',time,location) return GCRS coordinate of
mars observed at location on earth.
So difference vector between get_body('mars',time,loc1) and
get_body('mars',time,loc2) should be the same as differce vector between
loc1 and doc2.
Therefore difference vector between get_body('mars',time,loc1) and
get_body('mars',time,loc2) should be the same as difference vector between
get_body('jupiter',time,loc1) and get_body('jupiter',time,loc2).
But use following snippet,
from astropy.coordinates import
> EarthLocation,solar_system_ephemeris,get_body
> from astropy.time import Time
> import astropy.units as u
> planets=solar_system_ephemeris.bodies
> t=Time('2017-1-7')
> loc1=EarthLocation.of_site('ALMA')
> loc2=EarthLocation.of_site('BAO')
> with solar_system_ephemeris.set('jpl'):
> poses1=[]
> poses2=[]
> for i in range(len(planets)):
> poses1.append(get_body(planets[i],t,location=loc1).cartesian.xyz)
> poses2.append(get_body(planets[i],t,location=loc2).cartesian.xyz)
> print(poses2[i]-poses1[i])
get result:
[ 8063.95816843 7068.00850269 -6606.53423256] km
> [ 8224.04320343 7065.45624797 -6482.55365168] km
> [ 8064.42921932 7067.72318247 -6607.26674529] km
> [ 8266.19750362 7036.04863887 -6534.63230393] km
> [ 8025.04757395 6956.33442213 -6558.59139917] km
> [ 8064.08233562 7068.37313613 -6606.78203702] km
> [ 7979.54002401 6710.05480098 -6540.78743029] km
> [ 8766.62041795 5208.77094686 -6699.57502227] km
> [ 11237.56838802 6188.62185216 -5658.59566617] km
> [ 10447.75206614 304.28817022 -6981.0367673 ] km
> [ 6385.49008512 1293.04231977 -5061.7454344 ] km
The result is a list of very different vectors, it confused me very much.
Hope some one can help me?
Thanks
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