The History of the Calendar

Calendars help us keep track of time. People have used math to create calendars for thousands of years. They watched the Sun, Moon, and stars to figure out how long a year is and when seasons change.

Early Calendars

Ancient people noticed that the Moon goes through phases about every 29 or 30 days. They used this to create lunar calendars based on the Moon. Twelve Moon cycles gave them about 354 days.

But a solar year, the time it takes Earth to go around the Sun, is about 365 days. This mismatch caused problems. Ancient Egyptians were among the first to use a 365-day calendar.

The Calendar We Use Today

The calendar we use is called the Gregorian calendar. It was introduced by Pope Gregory XIII in 1582. It fixed errors in the older Julian calendar by changing the leap year rules.

The Gregorian calendar has 365 days in most years and 366 in leap years. This keeps the calendar lined up with the seasons. Most countries around the world use this calendar today.

Fun Facts

• The ancient Egyptian calendar had 12 months of exactly 30 days each, plus 5 extra days at the end.
• When the Gregorian calendar was adopted, some countries had to skip 10 days to catch up.
• The Chinese calendar is still used to set the date of Chinese New Year.

Did You Know?

A year is not exactly 365.25 days. It is closer to 365.2422 days. The Gregorian calendar uses a clever leap year rule to account for this tiny difference!