Description

Hello,

I found that c1.separation(c2) is different than c2.separation(c1) when c1 is CGRS with distance and c2 is ICRS.

Thanks!

Expected behavior

c1.separation(c2) is the correct value

Steps to Reproduce

import astropy.units as u
import astropy.coordinates as apc
c1=apc.SkyCoord("3h", "16d",frame="gcrs",  distance=4e5*u.km)
c2=apc.SkyCoord("7h", "7d")
c1.separation(c2)
c2.separation(c1)

System Details

Windows-10-10.0.19041-SP0
Python 3.7.6 (default, Jan 8 2020, 20:23:39) [MSC v.1916 64 bit (AMD64)]
Numpy 1.18.4
astropy 4.2
Scipy 1.4.1
Matplotlib 3.2.1