Source code for astropy.coordinates.builtin_frames.galactic

# 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 (
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 = """
    .. [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 <>`_.

[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.s), RepresentationMapping("d_y", "V", / u.s), RepresentationMapping("d_z", "W", / 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 *, dec=27.4 * _lon0_B1950 = Angle(123, # These are *not* from Reid & Brunthaler 2004 - instead, they were # derived by doing: # # >>> FK4NoETerms(ra=192.25*, dec=27.4* # # 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 *, dec=27.12825118085622 * _lon0_J2000 = Angle(122.9319185680026,