Other Time Scales
Julian day number is a count of days elapsed since Greenwich mean noon on 1 January 4713 B.C., Julian proleptic calendar. The Julian Date is the Julian day number followed by the fraction of the day elapsed since the preceding noon. Conveniently for astronomers, this avoids the date skip during an observation night.
Modified Julian day (MJD) is defined as MJD = JD - 2400000.5. An MJD day thus begins at midnight, civil date. Julian dates can be expressed in UT, TAI, TDT, etc. and so for precise applications the timescale should be specified, e.g. MJD 49135.3824 TAI.
Read more about this topic: Time Standard
Famous quotes containing the words time and/or scales:
“All questions rely on the present for their solution. Time measures nothing but itself. The word that is written may be postponed, but not that on the lip. If this is what the occasion says, let the occasion say it.”
—Henry David Thoreau (1817–1862)
“Love once
Tipped the scales but now is shadowed, invisible,
Though mysteriously present, around somewhere.”
—John Ashbery (b. 1927)