Julian calendar

Description

The Julian calendar was introduced by Julius Caesar in 45 BC. It was in common use until the 1500s, when countries started changing to the Gregorian calendar. However, some countries (for example, Greece and Russia) used it into the 1900s, and the Orthodox church in Russia still uses it, as do some other Orthodox churches.

In the Julian calendar, the tropical year is approximated as 365 1/4 days = 365.25 days. This gives an error of 1 day in approximately 128 years.

The approximation 365 1/4 is achieved by having 1 leap year every 4 years.

Note: The Julian Day Number has nothing to do with the Julian Calendar.

Gory details

Converting to and from the Julian calendar can be done using the Julian Day Number as an intermediat date representation. jdn_julian can be used to convert a Julian Day Number to an Julian date, while julian_jdn can be used to convert an Julian date to a Julian Day Number.

There's an extra routine available to correct an invalid Julian date. This routine is called julian_normdate and can be used in a variety of circumstances, Eg when you want to add a number of days or months to a date.

The names of the months are the same for the Julian and Gregorian calendar and can be determined using the julian_monthName routine.

Examples

In the following example julian_jdn is called to convert the Julian date April 12, 2001 to a Julian Day Number, jdn will have the value of 2452025.

jdn = julian_jdn(2001, 4, 12)

In the following example jdn_julian is called to convert the Julian Day Number 2452025 to an Julian date. After calling jdn_julian, year, month and day will have the values 2001, 4 and 12 respectively.

Call jdn_julian(2452025, year, month, day)

In the next example, julian_normDate is used to normalize a date, in this case the 29^th of Februari. If someYear is a leap year, month and day will not be changed, but for non-leap-years, month and day will become 3 and 1 respectively.

year=someYear
month=2
day=29
Call julian_normDate(year,month,day)

Is the next example, julian_monthName is called to determine the name of the third Julian (or civil) Month. monthname will have the value "March".

monthname = julian_monthName(3)

See also

julian_jdn, jdn_julian, julian_normDate, civil_monthName, Claus Tøndering's Calendar Faq

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