Angular Motion

by Dominic Ford, Editor
Last updated: 8 Aug 2023

The angular motion of an astronomical object is the rate at which it moves across the sky. This movement is due to the combination of the object's own motion through space, and the Earth's annual orbit around the Sun.

For solar system objects, this website reports the instantaneous rate of movement of the object across the sky, as seen from the observing site configured by the user (Fairfield). For objects which are very close to the Earth – most notably the Moon – this includes a substantial daily circular motion due to the observer's own rotational motion around the Earth's polar axis.

For stars, this website reports the star's proper motion, as measured by the Gaia spacecraft. This is the rate of movement of the object that would be observed by a hypothetical observer at the solar system's centre of mass, and excludes any annual parallax that the star may exhibit due to the Earth's orbital motion.





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