JulianDate

gives the current number of days since noon on November 24, 4714 BCE in the GMT time zone.

gives the number of days for the specified date.

gives the Julian date variant of the specified type.

JulianDate["type",date]

gives the variant for the specified date.

Details

In JulianDate[date], date can be a DateObject, a date string, a {y,m,d,h,m,s} date list, or a number corresponding to an absolute time specification.
JulianDate[date] assumes that the given date is in $TimeZone, unless it is a DateObject or TimeObject with an explicit TimeZone option value.
The result of JulianDate is a number of days, including a fractional part giving the time since the previous noon in GMT.
Shorter lists can be used in JulianDate[{y,m,…}]: {y} is equivalent to {y,1,1,0,0,0}, {y,m} to {y,m,1,0,0,0}, etc.
Values of m, d, h, m, s outside their normal ranges are appropriately reduced. Noninteger values of d, h, m, s can also be used.
Possible Julian date variants include:

	"Reduced"	relative to noon on November 16, 1858
	"Modified"	relative to midnight on November 17, 1858 (MJD)
	"Truncated"	relative to midnight on May 24, 1968 (TJD)
	"Dublin"	relative to noon on December 31, 1899 (DJD)
	"Full"	relative to noon on November 24, 4714 BCE (JD)

The default Julian date variant used is "Full". All referenced dates are using the proleptic Gregorian calendar.

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Julian date in days since noon November 24, 4714 BCE:

Julian date variants have different epoch dates:

Convert from a date object to a Julian date:

Convert from a date string to a Julian date:

Inputs are assumed to be in $TimeZone. Block can be used to specify a different input timezone:

Use DateObject to specify an input in a different TimeZone:

Separators are assumed if not specified:

Give explicit separators:

Date lists are converted to standard normalized form:

Day, hour, minute, and second values in input date lists can be noninteger:

The current year is used if not specified in a string:

JulianDate[date] converts date into Julian date format:

FromJulianDate converts from Julian date format into a DateObject expression:

Julian date 0 corresponds to this date in the proleptic Gregorian calendar for the GMT time zone:

It corresponds to noon January 1, in the Julian calendar for the GMT time zone:

Convert back to Julian date 0:

JulianDate is an affine transform of AbsoluteTime: rescale from seconds to days and add a constant:

Take any date:

Then this is an alternative way to compute Julian dates:

Introduced in 2015

(10.2)

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