What is the Julian calendar?

The Julian calendar was created by Roman emperor Julius Caesar in 45 BCE and is still the calendar commonly used today. This calendar consists of 365 days in every year, with 366 days in a year every four years, with an extra day added on to February.

Prior to the Julian calendar, the Romans had a date keeping system that involved a group decision of adding or removing dates on a calendar, making keeping track of time inconsistent. Caesar consulted Sosigenes, an Alexandrian astronomer, and devised a regular calendar system based on Earth and how it revolves around the sun.