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Utilities
Julian Day
Julian Day (JD) is continuous count of
days and fractions,
begined in January 1st, 4713 B.C. (-4712) at
Greenwich mean noon
(12h UT).
The Julian day method was invented by
Josefh Justus Scaliger and he
named it "Julian" in honor of his father Julius Scaliger.
This method is commomly used by astronomer in order to avoid the
complexity of the other
calendars.
Modified Julian Day (MJD) is JD - 2400000.5
Julian Ephemeris Day (JDE or JED) is the JD coresponds to an
instant of time measured in the
Terrestrial Dynamical Time scale.
Sidereal Julian Day is
Julian Day in which its days are
sidereal days instead of
mean solar days.
The Day of Week could be calculated from the JD
by taking the JD (of midnight) modulus 7 and adding 4 to
the result.
Read more (in Hebrew) about Julian day in the Hebrew Astropedia of the TAU AstroClub.
Constructed: November 1998, by: Eran Ofek