Calendars

Calendar systems and divisions

What makes up a calendar? Days, months and years, plus seasons and planets.

Calendarium, sounds familiar?

If time were an accountant, its most treasured object would be a calendar. After all, keeping count of when things happen is one of a calendar's functions.

This is shown by the very origin of the word, which goes back to ancient Rome. The closest Latin word is calendarium, meaning account book. Calendarium itself is derived from calendae or kalendae, the name for the first day of the month in Roman times.

Historically, calendars have been altered, corrected and sometimes completely redefined. A famous example is the switch from the Julian to the Gregorian calendar at the end of the 16th century.