Washington mean time Guide, Meaning , Facts, Information and Description
Washington mean time was the time observed at the US Naval Observatory at Washington, D.C It was sometimes called "Washington meridian time".The modern-day observatory code for the US Naval Observatory (before 1893) is 787, and the longitude was 77.0506°W. Thus the difference between Washington mean time and Greenwich Mean Time was 5 hours, 8 minutes, 12.1 seconds.
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 in Washington mean time to a modern-day GMT value it is necessary to add not 05:08:12.1 but 17:08:12.1 hours.