Calendar

As of Version 10.0, calendar functionality is built into the Wolfram Language »

Calendar

is an option for calendar functions that specifies which calendar system to use.

Details and Options

To use Calendar, you first need to load the Calendar Package using Needs["Calendar`"].
Calendar->system specifies to use calendar system system.
The following settings can be given:
Gregorian Gregorian calendar

Julian Julian calendar

Islamic Islamic calendar

Jewish Jewish calendar
With Calendar->Automatic, the Julian calendar is used before September 3, 1752, and the Gregorian calendar after September 13, 1752.

Wolfram Language code: Needs["Calendar`"]

Compute the number of days in the Islamic year 1420:

Wolfram Language code: DaysBetween[{1420, 1, 1}, {1421, 1, 1}, Calendar -> Islamic]

Wolfram Language code: Needs["Calendar`"]

Compute the number of days in the Jewish year 5760:

Wolfram Language code: DaysBetween[{5760, 7, 1}, {5761, 7, 1}, Calendar -> Jewish]

Wolfram Language code: Needs["Calendar`"]

In the Julian calendar, the year 1900 was a leap year:

Wolfram Language code: DateQ[{1900, 2, 29}, Calendar -> Julian]

This is not true in the standard (Gregorian) Western calendar:

Wolfram Language code: DateQ[{1900, 2, 29}]

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