555: Time Settings

The time settings option allows you to specify how the lengths of months are set. The default setting is the Gregorian calendar, which sets the lengths as follows:

January     31
February    28 (except for leap years when the length is 29)
March       31
April       30
May         31
June        30
July        31
August      31
September   30 (except for 1752 when the length is 19)
October     31
November    30
December    31

In the Gregorian calendar, leap years occur if the year is divisible by 4, but not by 100 unless also divisible by 400. Hence, 1900 is not a leap year, but 2000 is.

The Julian calendar is similar to the Gregorian except that September is always kept as 30 days, and leap years occur whenever the year is divisible by 4.

If leap years are ignored, all months have the same length as in the Julian calendar, and February is always set at 28 days. Ignoring leap years can be useful for pentad data since the year is always 365 days long, and thus divisible by 5.

Most dynamical models set all months to 30 days, and so an option is available to force CPT to adopt this convention.