GCRS

class astropy.coordinates.GCRS(*args, **kwargs)

Bases: astropy.coordinates.BaseCoordinateFrame

A coordinate or frame in the Geocentric Celestial Reference System (GCRS).

GCRS is distinct form ICRS mainly in that it is relative to the Earth’s center-of-mass rather than the solar system Barycenter. That means this frame includes the effects of abberation (unlike ICRS). For more background on the GCRS, see the references provided in the See Also section of the documentation. (Of particular note is Section 1.2 of USNO Circular 179)

This frame also includes frames that are defined relative to the Earth, but that are offset (in both position and velocity) from the Earth.

This frame has three frame attributes:

• obstime

  The time at which the observation is taken. Used for determining the position of the Earth.

• obsgeoloc

  3-vector giving the position of the observer relative to the center-of-mass of the Earth, oriented the same as BCRS/ICRS. Defaults to 0, meaning “true” GCRS.

• obsgeovel

  3-vector giving the celocity of the observer relative to the center-of-mass of the Earth, oriented the same as BCRS/ICRS. Defaults to 0, meaning “true” GCRS.

Parameters:

representation : BaseRepresentation or None

A representation object or None to have no data (or use the other keywords)

ra : Angle, optional, must be keyword

The RA for this object (dec must also be given and representation must be None).

dec : Angle, optional, must be keyword

The Declination for this object (ra must also be given and representation must be None).

distance : Quantity, optional, must be keyword

The Distance for this object along the line-of-sight. (representation must be None).

Attributes Summary

default_representation
frame_specific_representation_info
name
obsgeoloc
obsgeovel
obstime

Attributes Documentation

default_representation

frame_specific_representation_info

name = 'gcrs'

obsgeoloc = <Quantity [ 0., 0., 0.] m>

obsgeovel = <Quantity [ 0., 0., 0.] m / s>

obstime = <Time object: scale='utc' format='jyear_str' value=J2000.000>