(United States Naval Observatory)
(observatory obtaining astronomical data for Naval use)
The USNO (United States Naval Observatory)
is the USA's research facility to collect astronomical
data for use by the Navy and other branches of the military.
Navies and other sea travel have had a need for accurate astronomical
data for centuries, so such navy-related observatories are
It has carried out extensive astrometric surveys
producing catalogs (e.g., NOMAD)
and also measures and collates accurate and precise data about the Earth's
position, about time, about the expected positions of the Sun
and Moon, and about daylight, i.e., when and where it is present
over the Earth.
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Astrographic Catalog (AC)