Civil calendar

Description

The Civil or Gregorian calendar is the one commonly used today. It was proposed by Aloysius Lilius, a physician from Naples, and adopted by Pope Gregory XIII in accordance with instructions from the Council of Trent (1545-1563) to correct for errors in the older Julian Calendar. It was decreed by Pope Gregory XIII in a papal bull on 24 February 1582. This bull is named ``Inter Gravissimas'' after its first two words.

In the Civil or Gregorian calendar, the tropical year is approximated as 365 97/400 days = 365.2425 days. Thus it takes approximately 3300 years for the tropical year to shift one day with respect to the Gregorian calendar.

The approximation 365 97/400 is achieved by having 97 leap years every 400 years.

Gory details

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

There's an extra routine available to correct an invalid Civil date. This routine is called civil_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 Civil and Gregorian calendar and can be determined using the civil_monthName routine.

Examples

In the following example civil_jdn is called to convert the Civil date April 25, 2001 to a Julian Day Number, jdn will have the value of 2452025.

jdn = civil_jdn(2001, 4, 25)

In the following example jdn_Civil is called to convert the Julian Day Number 2452025 to an Civil date. After calling jdn_Civil, year, month and day will have the values 2001, 4 and 25 respectively.

Call jdn_Civil(2452025, year, month, day)

In the next example, Civil_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 Civil_normdate(year,month,day)

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

monthname = civil_monthName(3)

See also

civil_jdn, jdn_Civil, Civil_normdate, civil_monthName, Claus Tøndering's Calendar Faq

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