天体测量，将日心笛卡尔坐标转换为RA/D的问题

Question

我正试图用天文望远镜把日心笛卡尔矢量转换成RA/Dec。你知道吗

我从Skybot服务器得到了以下关于木星和小行星弗洛拉（8）在2019-10-11 00:00的位置的输出：

使用Astropy坐标包，我可以变换日心笛卡尔矢量Px，Py，Pz（x=-1.0394055704345，y=-5.1017277480665，z=-2.1859827838526）以匹配Skybot输出的RA/Dec（17 13 56.2541-22 46 31.024）。你知道吗

# Jupiter, Cartesian to ra/dec

from astropy.coordinates import SkyCoord

h = (-1.0394055704345,   -5.1017277480665,   -2.1859827838526) #Skybot Cartesian
Skybot_radec = '17 13 56.2541   -22 46 31.024'


helio = SkyCoord(x = h[0],   y =  h[1],  z = h[2],
                 unit='AU',
                 representation_type ='cartesian')

print('\nJupiter\nAstropy =    ', helio.to_string('hmsdms'))
print ('Skybot  =     ', Skybot_radec )

Skybot和Astropy给出了相同的结果：

>>>
Jupiter
Astropy =     17h13m56.2542s -22d46m31.0237s
Skybot  =     17 13 56.2541  -22 46 31.024

然而，尝试同样的过程与小行星弗洛拉的结果 在ra/dec中不匹配：

h = ( -0.217732049,  -2.230749006,  -0.848768038 ) #Skybot Cartesian
Skybot_radec = '16 25 19.6257   -19 37 54.618'


helio = SkyCoord(x = h[0],   y =  h[1],  z = h[2],
                 unit='AU',
                 representation_type='cartesian')


print('\nFlora\nAstropy =    ', helio.to_string('hmsdms'))
print ('Skybot  =    ', Skybot_radec )

>>>
Flora
Astropy =     17h37m42.0741s -20d44m27.5348s
Skybot  =     16 25 19.6257     -19 37 54.618

为什么它只适用于一种情况而不适用于另一种情况？你知道吗

针对Stuart在下面的评论，下面是包含GCRS帧和obstime的代码：

from astropy.coordinates import SkyCoord, GCRS
from astropy import units as u

obs_date = '2019-10-11 00:00'
h = ( -0.217732049,  -2.230749006,  -0.848768038 ) #Skybot cartesian
Skybot_radec = '16 25 19.6257   -19 37 54.618'


helio = SkyCoord(x = h[0],   y =  h[1],  z = h[2],
                               unit='AU',
                               frame = 'icrs',
                               representation_type='cartesian',
                               obstime = obs_date)

geo = helio.transform_to(GCRS(obstime = obs_date))

print('\nFlora\nAstropy =    ', geo.to_string('hmsdms'))
print ('Skybot  =    ', Skybot_radec )

## calculate object separation in the sky
Skybot_radec  = SkyCoord(Skybot_radec, frame = 'gcrs', unit = (u.hourangle, u.deg),
             obstime = obs_date)         
print('separation is ',Skybot_radec.separation(geo))

结果是：

Flora
Astropy =     16h20m00.3151s -19d17m49.5591s
Skybot  =     16 25 19.6257     -19 37 54.618
separation is  1d17m53.9205s

更接近，但仍有显著差异。有什么建议让它更接近吗？你知道吗