The word calendar comes from the Latin calendae, which referred to the first day of the month in the Roman calendar.

One of the earliest discovered calendars was found in Scotland and dates back approximately 10,000 years.

The Egyptians developed a 365-day calendar about 5,000 years ago.

The Babylonians, however, based their calendar on the moon. Their system later influenced both the Hebrews and the Arabs, as the Jewish and Islamic calendars are technically lunar.

The original Roman calendar had ten months and initially lacked a system for recording dates during the winter. When months were later added, they were placed in the middle of the calendar—resulting in months like October, originally the eighth month, becoming the tenth.

The Julian calendar, introduced by Julius Caesar, was highly accurate for its time until the more precise Gregorian calendar was introduced by Pope Gregory XIII.

The Russian Orthodox Church still follows the Julian calendar, which means Christmas is celebrated in January instead of December.

For a brief period, Sweden attempted to implement a February 30th.

France once adopted a revolutionary calendar featuring 10-day weeks and 12 months of 30 days.

The Babylonians were the first to introduce the concept of a seven-day week, which was later adopted by the Romans.

Most of the days of the week are named after Norse gods, such as Thor (Thursday) and Odin (Wednesday). However, Saturday is named after Saturn, the Roman god, while Sunday and Monday derive from the Sun and Moon, respectively.

Japan has a unique calendar system that resets whenever a new emperor ascends the throne.

North Korea uses a calendar system that begins with the birth of its first dictator, Kim Il-sung.

In the Islamic calendar, the day begins at sunset rather than midnight.

Babies born on Leap Day (February 29) are called leaplings. Depending on local customs, they may celebrate their birthday on either February 28 or March 1 in non-leap years.