Right Ascension & Declination: Observation, Measurement & Evidence

Right ascension and declination are equatorial coordinates used to specify directions on the celestial sphere in a way analogous to longitude and latitude on Earth.

Because the coordinate grid is tied to Earth's rotational axis projected onto the sky, a star's equatorial coordinates change only slowly from proper motion and from coordinate-frame effects such as precession, rather than changing hour by hour with local sky rotation.