Washington mean time
Encyclopedia
Washington mean time was the time at the meridian through the center of the old dome atop the main building at the old US Naval Observatory at Washington, D.C.
This Washington meridian
was defined on 28 September 1850 by the United States Congress
. The Old Naval Observatory is now on the grounds of the United States Navy Bureau of Medicine and Surgery, southwest of the corner of E and 23rd Streets in Foggy Bottom
(north of the Lincoln Memorial
). Washington mean time was sometimes called Washington meridian time. It was never used as the basis of any time zone, although it was the local mean time
of the city of Washington before the advent of American time zones on 18 November 1883. It was also used to time astronomical events by users of the American Ephemeris and Nautical Almanac
, first published for the year 1855.
In 1897, well after the Old Naval Observatory closed in 1892, the Coast and Geodetic Survey reported that its meridian was 77°3'2.3" west of Greenwich, which was quoted for the next 50 years in the list of observatories in the Almanac as . This old Washington meridian was repealed on 22 August 1912. A later version of Washington mean time based on the merdian of the clock room at the exact center of the New Naval Observatory (77°4'2.24"W or ) was still being used in 1950 on a few pages of the American Ephemeris and Nautical Almanac, even though most of its pages used Greenwich Civil Time, the American name for the midnight epoch Greenwich Mean Time. For astronomical purposes, before 1925 a day was considered to start at noon rather than the previous midnight. Thus to convert times of astronomical events before 1925 given in Washington mean time to modern Universal Time
it is necessary to add an additional 12 hours beyond the meridian difference from Washington to Greenwich, totalling more than 17 hours.
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....
This Washington meridian
Washington meridian
The Washington meridian was one of four prime meridians of the United States which passed through Washington, D.C.. The four which have been specified are:# through the Capitol# through the White House# through the old Naval Observatory...
was defined on 28 September 1850 by the United States Congress
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....
. The Old Naval Observatory is now on the grounds of the United States Navy Bureau of Medicine and Surgery, southwest of the corner of E and 23rd Streets in Foggy Bottom
Foggy Bottom
Foggy Bottom is one of the oldest late 18th and 19th-century neighborhoods in Washington, D.C. The area is thought to have received the name because its riverside location made it susceptible to concentrations of fog and industrial smoke, an atmospheric trait that did not prevent the neighborhood...
(north of the Lincoln Memorial
Lincoln Memorial
The Lincoln Memorial is an American memorial built to honor the 16th President of the United States, Abraham Lincoln. It is located on the National Mall in Washington, D.C. The architect was Henry Bacon, the sculptor of the main statue was Daniel Chester French, and the painter of the interior...
). Washington mean time was sometimes called Washington meridian time. It was never used as the basis of any time zone, although it was the local mean time
Local mean time
Local mean time is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude...
of the city of Washington before the advent of American time zones on 18 November 1883. It was also used to time astronomical events by users of the American Ephemeris and Nautical Almanac
American Ephemeris and Nautical Almanac
The American Ephemeris and Nautical Almanac was published for the years 1855 to 1980, containing information necessary for astronomers, surveyors, and navigators...
, first published for the year 1855.
In 1897, well after the Old Naval Observatory closed in 1892, the Coast and Geodetic Survey reported that its meridian was 77°3'2.3" west of Greenwich, which was quoted for the next 50 years in the list of observatories in the Almanac as . This old Washington meridian was repealed on 22 August 1912. A later version of Washington mean time based on the merdian of the clock room at the exact center of the New Naval Observatory (77°4'2.24"W or ) was still being used in 1950 on a few pages of the American Ephemeris and Nautical Almanac, even though most of its pages used Greenwich Civil Time, the American name for the midnight epoch Greenwich Mean Time. For astronomical purposes, before 1925 a day was considered to start at noon rather than the previous midnight. Thus to convert times of astronomical events before 1925 given in Washington mean time to modern Universal Time
Universal Time
Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...
it is necessary to add an additional 12 hours beyond the meridian difference from Washington to Greenwich, totalling more than 17 hours.
External links
- Position of the Observatory in Observations made during the year 1889 at the United States Naval Observatory (Washington: 1893) page XXII
- The Washington Refractor describing the present condition of the Old Naval Observatory
- Washington meridian marker stone at Meridian Hill Park in Washington, D.C.
- North Dakota's Boundaries Its western border is 27° west of the Washington meridian
- State lines and how they were surveyed