Julian calendar introduced The Julian calendar is a dating system established by Julius Caesar in 45 BC. It replaced the Roman Republician calendar, which was three months ahead of the solar calendar. The solar calendar represents the time it takes the earth to revolve around the sun (one full orbit takes the earth approximately 365 days, 5 hours, 48 minutes and 45 seconds to complete). To create a more standardised calendar, Caesar consulted the Alexandrian astronomer Sosigenes. Sosigenes divided the year into twelve months, all of which had either 30 or 31 days. The exception was February, which contained 28 days. He then created a leap year, including an extended February of 29 days, for every fourth year. However, there was no February 29 in the Julian calendar. Instead, in leap years, 23 February was repeated – there were two days of 23 February. To align the civic and solar calendars, Caesar added days to 46 BC, making it an extra long year of 445 days. Sosigenes had overestimated the length of the year by 11 minutes and 14 seconds, and by the mid 1500s his error had shifted the dates of the seasons by about 11 days from Caesar’s time. The Julian calendar became hopelessly out of sync with religious holidays such as Easter and fixed astronomical events such as equinoxes. In 1582, Pope Gregory XIII introduced the Gregorian calendar to address the cumulative inaccuracies of the Julian calendar. Gradually, the Julian calendar was abandoned in favour of this new calendar, which England officially adopted in 1752. Image Credits Roman Julian Calendar. Image ID: 2CF29JJ, agefotostock / Alamy Stock Photo Modern marble head of Julius Caesar, 18th century. Museum number: 1818,0110.3 © The Trustees of the British Museum, CC BY-NC-SA 4.0, portrait head | British Museum
