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API Reference — Stars and other distant objects

class skyfield.starlib.Star(ra=None, dec=None, ra_hours=None, dec_degrees=None, ra_mas_per_year=0.0, dec_mas_per_year=0.0, parallax_mas=0.0, radial_km_per_s=0.0, names=(), epoch=2451545.0)

The position in the sky of a star or other fixed object.

Each Star object specifies the position of a distant object. You should provide as a right ascension and declination relative to the ICRS (the recent improvement upon J2000). You can specify the coordinates using either floating point hours and degrees, or tuples that specify hour and degree fractions as minutes and seconds, or even full Skyfield Angle objects (which can themselves be initialized using hours, degrees, or radians):

>>> barnard = Star(ra_hours=17.963471675, dec_degrees=4.69339088889)
>>> barnard = Star(ra_hours=(17, 57, 48.49), dec_degrees=(4, 41, 36.20))
>>> barnard = Star(ra=Angle(hours=17.963471675),
...                dec=Angle(degrees=4.69339088889))

For objects whose proper motion across the sky has been detected, you can supply velocities in milliarcseconds (mas) per year, and even a parallax and radial velocity if those are known:

>>> barnard = Star(ra_hours=(17, 57, 48.49803),
...                dec_degrees=(4, 41, 36.2072),
...                ra_mas_per_year=-798.71,
...                dec_mas_per_year=+10337.77,
...                parallax_mas=545.4,
...                radial_km_per_s=-110.6)

See Stars and Distant Objects for a guide to using a Star once you have created it.