Source code for astropy.coordinates.builtin_frames.hcrs
# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
from __future__ import (absolute_import, unicode_literals, division,
print_function)
from ..frame_attributes import TimeFrameAttribute
from .utils import DEFAULT_OBSTIME
from .baseradec import _base_radec_docstring, BaseRADecFrame
[docs]class HCRS(BaseRADecFrame):
"""
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 :ref:`astropy-coordinates-seealso` section of
the documentation.
The frame attributes are listed under **Other Parameters**.
{params}
Other parameters
----------------
obstime : `~astropy.time.Time`
The time at which the observation is taken. Used for determining the
position of the Sun.
"""
obstime = TimeFrameAttribute(default=DEFAULT_OBSTIME)
HCRS.__doc__ = HCRS.__doc__.format(params=_base_radec_docstring)
# Transformations are defined in icrs_circ_transforms.py