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Astronomy Day is an annual event intended to provide a means of interaction between the general public and various astronomy enthusiasts, groups and professionals.

This event was started in 1973 by Doug Berger, the president of the Astronomical Association of Northern California. His intent was to set up various telescopes in busy urban locations so that passersby could enjoy views of the heavens. Since then the event has expanded and is now sponsored by a number of organizations associated with astronomy.

Astronomy Day also forms part of Astronomy Week, which begins on the preceding Monday.

Originally, Astronomy Day occurred on a Saturday between mid-April and mid-May, and was scheduled so as to occur at or close to the first quarter Moon. In 2007, an autumn rendition of Astronomy Day was added. It was scheduled to occur on a Saturday between mid-September and mid-October so as to be on or close to the first quarter Moon.

The lunar influence on the schedule means that the events happen on a different date each year, rather than set calendar dates.