Dave Rolsky edited this page Jan 30, 2017 · 3 revisions


Dates and times are a complex subject, and this site only covers a fraction of it. See these resources for more details.


Calendrical Calculations, by Edward M. Reingold and Nachum Dershowitz

  • This book contains algorithms for many different calendars, both modern and historical. The book has a website.

Online Resources

  • The Many Dates and Times of Perl - An article by Dave Rolsky on which specifically addresses datetime manipulation in Perl. The article includes a fairly comprehensive list of non-DateTime project Perl modules that deal with dates and/or times.
  • Claus Tondering's calendar FAQ - This faq covers topics such as the astronomical events on which some calendars are based, the Julian and Gregorian calendars' usage and history, and explains how a number of other calendars work, such as the French Revolutionary and Mayan calendars.
  • - This site has lots of good date and time information. The exhibits links are all interesting.
  • ISO 8601 Final Draft - This is a downloadable PDF version of the final draft of ISO 8601. ISO 8601 is a standard defining representations for datetime and time periods. Many applications implement these standards, so it is worth reading. Also see the dmoz ISO 8601 category.
  • RFC 2445 - the iCalendar RFC.
  • Olson Time Zone database - Information on the Olson time zone database. This is the standard time zone database used in computing, and is the one used by the DateTime::TimeZone module.
  • About Daylight Saving Time - a comprehensive history and explanation of the Daylight Saving Time system.
  • Universal Time on Wikipedia - An explanation of what Universal Time is.
  • The Best of Dates, the Worst of Dates - This contains some of the history of calendars and time calculations, but also discusses some common mistakes made by programmers when dealing with dates and times.