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
# through the new Naval Observatory.

Their longitudes may be reported in three ways:
# relative to the local vertical used by astronomic observations
# relative to NAD 27 (North American Datum 1927), an ellipsoid of revolution tangent to mean sea level at triangulation station Meade's Ranch, Kansas (not earth-centered);
# relative to NAD 83, an earth-centered ellipsoid of revolution whose dimensions are chosen to minimize the undulations of the geoid (world-wide mean sea level; to less than 100 m).


Pierre (Peter) Charles L'Enfant specified the first meridian in his 1791 "Plan of the city intended for the permanent seat of the government of the United States . . .". [ [http://www.loc.gov/exhibits/treasures/tri001.html Pierre Charles L'Enfant's 1791 "Plan of the city intended for the permanent seat of the government ...."] "in" [http://www.loc.gov official website of the U.S. Library of Congress] Accessed August 13, 2008. Freedom Plaza in downtown Washington, D.C., contains an inlay of the central portion of L'Enfant's plan.] (Shortly after L'Enfant prepared this plan, its subject received the name "City of Washington".) His plan stated that the meridian of the Congress House, now called the Capitol, would be nowrap|0°0'. The center of its dome (completed in 1863 during the Civil War) was recently measured by the National Geodetic Survey to be nowrap|77°0'21.9"W (NAD 83).

White House

L'Enfant planned Washington around a right triangle, having its 90° vertex at the Washington Monument, its eastern vertex at the Congress House, and its northern vertex at the President's House, now called the White House. The west side of L'Enfant's triangle forms a natural prime meridian passing through the President's House. The following five features on this meridian are listed from south to north. In 1793, Secretary of State Thomas Jefferson surveyed and marked with a wooden post the southwest vertex of L'Enfant's triangle, establishing the second Washington meridian, the one through the President's House. The wooden post was replaced by the "Jefferson Pier" in 1804, while Jefferson was President of the United States. After removal and replacement several times, it was permanently replaced in 1889 by a two foot (0.7 m) square, two foot tall granite pier, now 119 m WNW of the center of the Washington Monument. Its longitude is nowrap|77°2'11.56"W (NAD 83). In 1890, the "Meridian Stone" was placed at the center of the Ellipse on the same meridian. It is an 18 inch (45 cm) square granite post set flush with the ground. In 1923, the "Zero Milestone" was placed on the same meridian on the north side of the Ellipse, intended to represent the zero mileage point for all United States roads (but never was). It is a granite pillar about 18 inches (45 cm) square and about 3.5 feet (1 m) tall. The most prominent feature on this Washington meridian (besides the White House) is 16th Street, which extends due north from the White House. The last feature on this meridian no longer exists. It was a small freestone obelisk placed in 1804 on top of a hill 1.5 miles (2.5 km) north of the President's House, hence the name "Meridian Hill". It was at the northern end of 16th Street, north of Florida Avenue, before 16th Street was extended northward soon after 1900, covering it up. Now adjoining the east side of 16th Street where the obelisk once stood is Meridian Hill Park.

Old Naval Observatory

The third meridian was defined on 28 September 1850 by Congress: " [T] he meridian of the observatory at Washington shall be adopted and used as the American meridian for all astronomical purposes, and ... the meridian of Greenwich shall be adopted for all nautical purposes." [9 "Statutes at Large" 515] The observatory decided that this meridian passed through the center of the original (small) dome atop the main building of the "Old Naval Observatory", 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 and west of the White House). The observatory adopted nowrap|77°2'48.0"W for its meridian in the "American Ephemeris and Nautical Almanac" for the years 1855 to 1869 (as nowrap|5h8m11.2s). In 1897, well after the observatory closed in 1892, the Coast and Geodetic Survey reported that its meridian was nowrap|77°3'2.3" west of Greenwich, [3618 "Serial Set" 254] which was quoted for the next 50 years in the list of observatories in the "Almanac" (as nowrap|5h8m12.15s). When referred to later datums, this meridian has been variously specified as nowrap|77°3'6.119"W or nowrap|77°3'6.276"W (both presumably NAD 27). The first would be nowrap|77°3'5.037"W (NAD 83). This meridian was repealed by Congress on 22 August 1912 to allow the Greenwich meridian to become the legal prime meridian of the United States.

Western state borders

Many western states have borders that are meridians of "longitude west of Washington", that is, west of the legal 1850 meridian through the Old Naval Observatory. However, their present boundaries follow the subsequently surveyed boundary, even when inaccurately marked a few miles (kilometers) east or west of the meridian in the statute. Other western states have meridians relative to Greenwich (Alaska, California, Oklahoma, Texas) or relative to a river or lake (Arkansas, Louisiana, Minnesota, Missouri, Oregon, Washington).

The following meridians west of Washington are listed east to west, along with the appropriate boundary of the present state. The date of the meridian's definition is in parentheses (all in the 1860s). All states were territories of the same name when their meridians were specified except as noted. States without dates have boundaries dependent on the neighboring state with a date listed immediately above it.

New Naval Observatory

The fourth meridian was through the clock room of the new Naval Observatory, 2.3 miles (3.8 km) northwest of the White House, at nowrap|77°3'56.7"W (1897) or nowrap|77°4'2.24"W (NAD 27) or nowrap|77°4'1.16"W (NAD 83). The clock room is a small building at the exact center of the 1000-foot (305 m) radius observatory grounds, whose northern entrance is at 34th Street and Massachusetts Avenue. It was used in the "Almanac" for the years 1898–1950 as the independent variable of time for a few tables (even though Washington's civil time since 1883 had been that of the standard time zone GMT − 5 hours (75°W)).


* Joseph Hyde Pratt, "American Prime Meridians", "Geographical Review" 32 (1942) 233-244.
* Franklin K. Van Zandt, "Boundaries of the United States and the several states", Geological Survey Professional Paper 909 (1976)
* "American ephemeris and nautical almanac" (Washington, DC: annual), preface and observatories

ee also

* Washington mean time
* Willamette Stone

External links

* [http://www.savethemall.org/mall/resource-hist02.html The 1791 L'Enfant plan and the Mall]
* [http://www.exploredc.org/index.php?id=3 Map of L'Enfant's Plan]
* [http://geodesy.noaa.gov/PUBS_LIB/WashMon.pdf Washington Monument GPS Project] including Jefferson Pier and Zero Milestone (1.29 MB)
* [http://terraserver.microsoft.com/addressimage.aspx?t=4&s=9&lon=-77.0513873533333&lat=38.89503269&alon=-77&alat=38 Old Naval Observatory] Old dome at center, 23rd Street at right.
* [http://www.labbey.com/Telescopes/Washington.html Washington Refractor] describing present condition of Old Naval Observatory
* [http://www.ngs.noaa.gov/INFO/Washmon/info.htm Washington Monument GPS Height Modernization Project] listing coordinates of Jefferson Pier, Meridian Stone, and Zero Milestone (click on names for photos)

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