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Astronomical Information Center

Moon Phases Image

This US Naval Observatory Website is undergoing modernization and will be offline starting Thursday, 24 October 2019. The expected completion of work and return of service is estimated as 30 April 2020. Please visit and submit a Requirements Form to the USNO PAO if the information you are seeking is not accessible via another means.

Glossary of Terms

Phenomena of the Sun and Moon


Calendars and Historical Events

Computing Astronomical Data and Phenomena

Celestial Navigation

Other Topics

Links to Information at Other Sites