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:
“You need an infinite stretch of time ahead of you to start to think, infinite energy to make the smallest decision. The world is getting denser. The immense number of useless projects is bewildering. Too many things have to be put in to balance up an uncertain scale. You can’t disappear anymore. You die in a state of total indecision.”
—Jean Baudrillard (b. 1929)
“For these have governed in our lives,
And see how men have warred.
The Cross, the Crown, the Scales may all
As well have been the Sword.”
—Robert Frost (1874–1963)