Washington Meridian
The Washington meridians are four meridians that were used as prime meridians in the United States and pass 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 that is at mean sea level beneath triangulation station Meades Ranch, Kansas (not earth-centered);
- relative to NAD 83, an earth-centered ellipsoid of revolution with dimensions chosen to best fit the undulating (±100 m) geoid (world-wide mean sea level).
NAD83 longitude of the Capitol is about 1.1 arc seconds less than its NAD27 longitude; astronomic longitude there is about 4 arc seconds less than NAD83.
Read more about Washington Meridian: Capitol Meridian, White House Meridian, Old Naval Observatory Meridian, New Naval Observatory Meridian
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