pm_icrs_to_gal

gala.coordinates.pm_icrs_to_gal(coordinate, pm)[source]

Convert proper motion in ICRS coordinates (RA, Dec) to Galactic coordinates (l,b).

Parameters:

coordinate : SkyCoord, BaseCoordinateFrame

An instance of an Astropy coordinate object. Can be in any frame that is transformable to ICRS coordinates.

pm : Quantity, iterable

Full description of proper motion in Right ascension (RA) and declination (Dec). Can either be a tuple of two Quantity objects or a single Quantity with shape (2,N). The proper motion in RA is assumed to be multipled by cosine of declination, \(\mu_\alpha\cos\delta\).
Returns:

pm : Quantity

An astropy Quantity object specifying the proper motion vector array in Galactic coordinates. Will have shape (2,N).

Examples

>>> import astropy.units as u
>>> import astropy.coordinates as coord
>>> c = coord.SkyCoord(ra=196.5*u.degree, dec=-10.33*u.deg, distance=16.2*u.kpc)
>>> pm = [-1.84741767, 3.34334366]*u.mas/u.yr
>>> pm_icrs_to_gal(c, pm) 
<Quantity [-1.52999988, 3.49999973] mas / yr>