United States Naval Observatory (USNO)

A United States Navy scientific institution providing astronomical, Earth-orientation and precise-time data.

USNO maintains time standards and produces astronomical observations, reference data and publications supporting navigation, positioning, defence and science. It jointly produces the Nautical Almanac with HM Nautical Almanac Office.

Its services provide reference information rather than a complete onboard navigation method; users must select the correct time scale, coordinates, publication and calculation procedure.