# Licensed under a 3-clause BSD style license - see LICENSE.rst
from astropy import units as u
from astropy.coordinates import representation as r
from astropy.coordinates.angles import Angle
from astropy.coordinates.baseframe import (
BaseCoordinateFrame,
RepresentationMapping,
base_doc,
)
from astropy.utils.decorators import format_doc
from .fk4 import FK4NoETerms
# these are needed for defining the NGP
from .fk5 import FK5
__all__ = ["Galactic"]
doc_components = """
l : `~astropy.coordinates.Angle`, optional, keyword-only
The Galactic longitude for this object (``b`` must also be given and
``representation`` must be None).
b : `~astropy.coordinates.Angle`, optional, keyword-only
The Galactic latitude for this object (``l`` must also be given and
``representation`` must be None).
distance : `~astropy.units.Quantity` ['length'], optional, keyword-only
The Distance for this object along the line-of-sight.
pm_l_cosb : `~astropy.units.Quantity` ['angular speed'], optional, keyword-only
The proper motion in Galactic longitude (including the ``cos(b)`` term)
for this object (``pm_b`` must also be given).
pm_b : `~astropy.units.Quantity` ['angular speed'], optional, keyword-only
The proper motion in Galactic latitude for this object (``pm_l_cosb``
must also be given).
radial_velocity : `~astropy.units.Quantity` ['speed'], optional, keyword-only
The radial velocity of this object.
"""
doc_footer = """
Notes
-----
.. [1] Blaauw, A.; Gum, C. S.; Pawsey, J. L.; Westerhout, G. (1960), "The
new I.A.U. system of galactic coordinates (1958 revision),"
`MNRAS, Vol 121, pp.123 <https://ui.adsabs.harvard.edu/abs/1960MNRAS.121..123B>`_.
"""
[docs]@format_doc(base_doc, components=doc_components, footer=doc_footer)
class Galactic(BaseCoordinateFrame):
"""
A coordinate or frame in the Galactic coordinate system.
This frame is used in a variety of Galactic contexts because it has as its
x-y plane the plane of the Milky Way. The positive x direction (i.e., the
l=0, b=0 direction) points to the center of the Milky Way and the z-axis
points toward the North Galactic Pole (following the IAU's 1958 definition
[1]_). However, unlike the `~astropy.coordinates.Galactocentric` frame, the
*origin* of this frame in 3D space is the solar system barycenter, not
the center of the Milky Way.
"""
frame_specific_representation_info = {
r.SphericalRepresentation: [
RepresentationMapping("lon", "l"),
RepresentationMapping("lat", "b"),
],
r.CartesianRepresentation: [
RepresentationMapping("x", "u"),
RepresentationMapping("y", "v"),
RepresentationMapping("z", "w"),
],
r.CartesianDifferential: [
RepresentationMapping("d_x", "U", u.km / u.s),
RepresentationMapping("d_y", "V", u.km / u.s),
RepresentationMapping("d_z", "W", u.km / u.s),
],
}
default_representation = r.SphericalRepresentation
default_differential = r.SphericalCosLatDifferential
# North galactic pole and zeropoint of l in FK4/FK5 coordinates. Needed for
# transformations to/from FK4/5
# These are from the IAU's definition of galactic coordinates
_ngp_B1950 = FK4NoETerms(ra=192.25 * u.degree, dec=27.4 * u.degree)
_lon0_B1950 = Angle(123, u.degree)
# These are *not* from Reid & Brunthaler 2004 - instead, they were
# derived by doing:
#
# >>> FK4NoETerms(ra=192.25*u.degree, dec=27.4*u.degree).transform_to(FK5())
#
# This gives better consistency with other codes than using the values
# from Reid & Brunthaler 2004 and the best self-consistency between FK5
# -> Galactic and FK5 -> FK4 -> Galactic. The lon0 angle was found by
# optimizing the self-consistency.
_ngp_J2000 = FK5(ra=192.8594812065348 * u.degree, dec=27.12825118085622 * u.degree)
_lon0_J2000 = Angle(122.9319185680026, u.degree)