Gregorian calendar: 8 things you need to know

A good grasp of the Gregorian calendar is fundamental for our daily routines and time management, as it forms the cornerstone of most everyday activities and global official record-keeping. Some key things to know about the Gregorian calendar:

Pope Gregory XIII (born Ugo Boncompagni in 1502) who introduced the “Gregorian” calendar in 1582. Until then, the Julian calendar had been in use since 45 BC. The Gregorian calendar is also called the "New Style" or Western|Christian calendar, and is based on the solar dating system. It was initially followed by a number of European countries. Today, the Gregorian calendar is the most widely-used civil calendar in the world.

It was introduced as a reform of the Julian calendar, which had minor miscalculations of the solar year's length by 11 minutes, and had gradually fallen out of alignment with the changing seasons.

For example, this resulted in the date of the Easter, traditionally celebrated around March 21, drifting farther from the spring equinox with each passing year. The Gregorian calendar sorted a discrepancy in the Julian calendar that threw the calendar year off from the solar year by 10 days.

The Julian calendar was introduced by Roman emperor Julius Caesar in the year 45 BC. The year 46 B.C. lasted 445 days and later became known as the "final year of confusion.” The Julian calendar was in use for nearly 1600 years, before the Gregorian calendar started supplanting it in 1582.

The Gregorian calendar has 12 months, just like its predecessor, the Julian calendar. The months are January, February, March, April, May, June, July, August, September, October, November, and December.

The Gregorian year has an average length of 365.2425 days, which is close to the solar year of approximately 365.2422 days.

It was only in 1752 — about 170 years after it was proclaimed by Gregory XIII — when England adopted the Gregorian calendar. When it was introduced, Benjamin Franklin (who lived in London) wrote, "It is pleasant for an old man to be able to go to bed on Sept. 2, and not have to get up until Sept. 14." Nearly two weeks evaporated into thin air in England when it transitioned from the Julian calendar, which had left the country 11 days behind much of Europe.

While the Gregorian calendar is the international standard for civil purposes, various cultures and religions use their own calendars for religious or cultural events, creating a rich tapestry of diverse ways to measure time.