# HCRS¶

class astropy.coordinates.HCRS(*args, copy=True, representation_type=None, differential_type=None, **kwargs)[source]

A coordinate or frame in a Heliocentric system, with axes aligned to ICRS.

The ICRS has an origin at the Barycenter and axes which are fixed with respect to space.

This coordinate system is distinct from ICRS mainly in that it is relative to the Sun’s center-of-mass rather than the solar system Barycenter. In principle, therefore, this frame should include the effects of aberration (unlike ICRS), but this is not done, since they are very small, of the order of 8 milli-arcseconds.

For more background on the ICRS and related coordinate transformations, see the references provided in the See Also section of the documentation.

The frame attributes are listed under Other Parameters.

Parameters: Other Parameters: data : BaseRepresentation subclass instance A representation object or None to have no data (or use the coordinate component arguments, see below). 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). pm_ra_cosdec : Quantity, optional, must be keyword The proper motion in Right Ascension (including the cos(dec) factor) for this object (pm_dec must also be given). pm_dec : Quantity, optional, must be keyword The proper motion in Declination for this object (pm_ra_cosdec must also be given). radial_velocity : Quantity, optional, must be keyword The radial velocity of this object. representation_type : BaseRepresentation subclass, str, optional A representation class or string name of a representation class. This sets the expected input representation class, thereby changing the expected keyword arguments for the data passed in. For example, passing representation_type='cartesian' will make the classes expect position data with cartesian names, i.e. x, y, z in most cases. differential_type : BaseDifferential subclass, str, dict, optional A differential class or dictionary of differential classes (currently only a velocity differential with key ‘s’ is supported). This sets the expected input differential class, thereby changing the expected keyword arguments of the data passed in. For example, passing differential_type='cartesian' will make the classes expect velocity data with the argument names v_x, v_y, v_z. copy : bool, optional If True (default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument. obstime : Time The time at which the observation is taken. Used for determining the position of the Sun.

Attributes Summary

Attributes Documentation

default_differential
default_representation
frame_attributes = {'obstime': <astropy.coordinates.attributes.TimeAttribute object at 0x7f3878bbc7f0>}
frame_specific_representation_info
name = 'hcrs'
obstime = <Time object: scale='utc' format='jyear_str' value=J2000.000>