Founded in 1919 to promote and safeguard the science of astronomy. The organization is also the internationally recognized authority for classifying celestial bodies and their surface features.

Computes the position, brightness, and other observable characteristics of celestial bodies, as well as the circumstances of astronomical phenomena. Includes information on calendars and related topics.

Resources, searchable forums and searchable lists of organizations providing astronomy services.

Information and articles on astronomy, space and related topics. Also features a friendly forum and a telescope buyer's FAQ page.

Contains 3D maps of the universe zooming out from the nearest stars to the scale of the galaxy and out to the surrounding superclusters and finally to the scale of the known universe.

Facts and statistical information about planets, moons, constellations, stars, galaxies, and Messier objects.