Editing United States Naval Observatory (section)

=== History of the time service ===
By the early 1870s the USNO daily noon-time signal was distributed electrically, nationwide, via the [[Western Union]] Telegraph Company. Time was also "sold" to the railroads<ref>{{cite book | last=Bartky | first=Ian R. | title=Selling the True Time | publisher=Stanford University Press | publication-place=Stanford, Calif | date=2000 | isbn=978-0-8047-3874-3 | page=199}}</ref> and was used in conjunction with [[railroad chronometer]]s to schedule American rail transport. Early in the 20th&nbsp;century, the service was broadcast by radio, with Arlington time signal available to those with [[wireless]] receivers.

In November&nbsp;1913 the [[Paris Observatory]], using the [[Eiffel Tower]] [[Eiffel Tower#Communications|as an antenna]], exchanged sustained wireless (radio) signals with the U.S.&nbsp;Naval Observatory to determine the exact difference of longitude between the two institutions, via an antenna in [[Arlington County, Virginia|Arlington, Virginia]].<ref>{{cite news |title=Paris time by wireless |date=22 November 1913 |newspaper=[[The New York Times]] |page=1}}</ref>

The U.S. Naval Observatory in Washington continues to be a major authority in the areas of [[Precise Time and Time Interval]], [[Earth Orientation Parameters|Earth orientation]], [[astrometry]], and celestial observation. In collaboration with many national and international scientific establishments, it determines the timing and astronomical data required for accurate [[navigation]], [[astrometry]], and fundamental [[astronomy]], and [[Naval Observatory Vector Astrometry Subroutines|calculation methods]] — and distributes this information (such as [[Star catalogue|star catalogs]])<ref>{{cite web |publisher=Naval Meteorology and Oceanography Command |title=Catalog information |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/astrometry/information/catalog-info |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726022418/http://www.usno.navy.mil/USNO/astrometry/information/catalog-info |url-status=dead }}</ref> on-line and in the annual publications ''[[The Astronomical Almanac]]'' and ''[[The Nautical Almanac]]''.<ref>{{cite web |publisher=Naval Meteorology and Oceanography Command |title=Interactive catalog and image search |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/icas/fchpix |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726022359/http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/icas/fchpix |url-status=dead }}</ref>

Former USNO director [[Gernot M. R. Winkler]] initiated the "[[Master clock]]" service that the USNO still operates,<ref>{{cite web |title=USNO Master Clock |url=http://www.usno.navy.mil/USNO/time/master-clock/ |access-date=2011-07-27 |website=usno.navy.mil |series=Naval Oceanography Portal |archive-date=2010-12-07 |archive-url=https://web.archive.org/web/20101207082711/http://www.usno.navy.mil/USNO/time/master-clock |url-status=dead }}</ref><ref>{{cite web |url=http://www.usno.navy.mil/USNO/time/master-clock/ |archive-url=https://web.archive.org/web/20220120185645/http://www.usno.navy.mil/USNO/time/master-clock/ |archive-date=2022-01-20 |title=USNO Master Clock — Naval Oceanography Portal}}</ref> and which provides [[Atomic clock|precise time]] to the [[GPS satellite blocks|GPS satellite]] constellation run by the [[United States Space Force]]. The alternate Master Clock time service continues to operate at [[Schriever Space Force Base]] in [[Colorado]].