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A modified version of the Julian date denoted MJD obtained by subtracting 2,400,000.5 days
from the Julian date JD,
The MJD therefore gives the number of days since midnight on November 17, 1858. This date
corresponds to 2400000.5 days after day 0 of the Julian calendar. MJD is still in common usage in
tabulations by the U. S. Naval Observatory. Care is needed in converting to other time units, however, as a result of
the half day offset (unlike the Julian date, the modified Julian date is referenced to midnight
instead of noon) and because of the insertion of semiannual leap seconds (which are
inserted at midnight).
The following table gives the modified Julian date for the "zeroth" of each month at 0 UT.
So add
 to get the Julian date of a given day D of the month at a given time  .
| Month |
1997 |
1998 |
1999 |
2000 |
| January |
5 0448 |
5 0813 |
5 1178 |
5 1543 |
| February |
5 0479 |
5 0844 |
5 1209 |
5 1574 |
| March |
5 0507 |
5 0872 |
5 1237 |
5 1603 |
| April |
5 0538 |
5 0903 |
5 1268 |
5 1634 |
| May |
5 0568 |
5 0933 |
5 1298 |
5 1664 |
| June |
5 0599 |
5 0964 |
5 1329 |
5 1695 |
| July |
5 0629 |
5 0994 |
5 1359 |
5 1725 |
| August |
5 0660 |
5 1025 |
5 1390 |
5 1756 |
| September |
5 0691 |
5 1056 |
5 1421 |
5 1787 |
| October |
5 0721 |
5 1086 |
5 1451 |
5 1817 |
| November |
5 0752 |
5 1117 |
5 1482 |
5 1848 |
| December |
5 0782 |
5 1147 |
5 1512 |
5 1878 |
 Julian Date
Montenbruck, O. and Pfleger, T. "Calendar and Julian Dates." §2.2 in Astronomy on the Personal Computer, 4th ed.
Berlin: Springer-Verlag, pp. 14-17, 2000.
United States Government Printing Office. The Astronomical Almanac for the Year 2000.
Washington, DC: Navy Dept., Naval Observatory, Nautical Almanac Office, p. B4, 2000.
© 1996-2007 Eric W. Weisstein
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