Calendars' facets

Climatology, and climate simulations, routinely use calendars different from the everyday Western Gregorian calendar. For example, to ease the calculation of various conserved or diagnostic quantities, 360 day years with 12 months of 30 days are often used.

There is also the understandable confusion over using calendars for Western dates about 300 years ago, when the Julian calendar was abandoned, the Gregorian adopted, and "everyone lost 11 days of their lives". This switch was in different years in different countries. Some of this confusion can be avoided by extending the Gregorian calendar backwards to dates before its introduction. This is the Proleptic Gregorian Calendar.

There are also many other completely different calendars, such as Chinese, Hindu, Jewish, Muslim, Parsi, etc. These cannot be avoided completely as some climatological research involves extracting information from old or ancient records.

Hidden in these calendar definitions are the issues of scope and precision. Is the calendar solar, stellar (sidereal), lunar or a combination? How often and when are intercalations made, such as leap seconds, days, weeks or months?

There are also the issues around confusing calendars (e.g. Julian), temporal reference systems (e.g. milliseconds since midnight, 1st January 1970) and notation (e.g. ISO8601:2004).

-- PieroCampalani - 09 Apr 2013 (from Chris Little's email, 18 Mar 2013)