# Modified Julian Day (MJD)

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This equation gives you the Modified Julian Day (MJD) when you input a Gregorian (standard modern calendar date).

The MJD's starting point epoch is midnight on November 17, 1858.

"The Modified Julian Date (MJD) was introduced by the Smithsonian Astrophysical Observatory in 1957 to record the orbit of Sputnik via an IBM 704 (36-bit machine) and using only 18 bits until August 7, 2576. MJD is the epoch of OpenVMS, using 63-bit date/time, postponing the next Y2K campaign to July 31, 31086, 02:48:05.47."1

# Example

If you input January 1, 2000, this equation will return the Julian Day:  51544.5

If you input November 17, 1858, this equation will return the Julian Day: 0.5