# ICRS¶

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

A coordinate or frame in the ICRS system.

If you’re looking for “J2000” coordinates, and aren’t sure if you want to use this or FK5, you probably want to use ICRS. It’s more well-defined as a catalog coordinate and is an inertial system, and is very close (within tens of milliarcseconds) to J2000 equatorial.

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

Parameters
dataBaseRepresentation subclass instance

A representation object or None to have no data (or use the coordinate component arguments, see below).

raAngle, optional, must be keyword

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

decAngle, optional, must be keyword

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

distanceQuantity, optional, must be keyword

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

pm_ra_cosdecQuantity, 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_decQuantity, optional, must be keyword

The proper motion in Declination for this object (pm_ra_cosdec must also be given).

radial_velocityQuantity, optional, must be keyword

The radial velocity of this object.

representation_typeBaseRepresentation 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 unless overriden via frame_specific_representation_info. To see this frame’s names, check out <this frame>().representation_info.

differential_typeBaseDifferential 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 unless overriden via frame_specific_representation_info. To see this frame’s names, check out <this frame>().representation_info.

copybool, optional

If True (default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument.

Attributes Summary

Attributes Documentation

default_differential
default_representation
frame_specific_representation_info
name = 'icrs'