Leap Year

Fact!

Caesar reformed the imprecise Roman calendar into the 12-month, 365 day format that we use today.

Fact #4

Except for those special "00" years, leap years always fall on years whose last 2 digits are divisible by 4, like 2004, 2008, 2012, and so on.

In what year did he make the change?

In 1582.

In which calendar did he make that change?

In the Gregorian calendar.

How many days did the year 1752 have in Great Britain and the United States?

It had only 354 days, September 14 fell one day after September 2.

What was the problem with his calendar?

It was that the calendar year still didn't match up with the solar year. Because of the error, the calendar was still gaining a full day every 128 years. After more than a thousand years, the extra day would begin to add up.

Who made this practice official?

Julius Caesar, the Roman dictator, in 45 B.C.E.

Fact #6

Many cultures calculate the days of festivals and religious observances with older, traditional calendars. Those calendars deal with leap years in different ways. Like, the months on the traditional Chinese calendar and Hebrew calendar, are based on the cycle of the moon. There are 12 short months, and an extra month is inserted every 2 or 3 years to keep things orderly.

What day was the vernal equinox supposed to fall on?

March 21, but by the late 1500s, it was moving closer and closer to February.

Who announced that every 4 years there would be a leap year?

Pope Gregory XIII.

Fact #5

The Gregorian calendar was adopted at different times in different countries. To re-set the vernal equinox at March 21, some countries dropped days off of the calendar.

What is the vernal equinox?

The first day of spring.

Fact #2

The lost time made it hard to set the dates of religious festivals.

Fact #3

The system we use today is still not perfect, the calendar still loses a day every 3,200 years or so.

Why do we have leap years?

The time it takes the earth to make one complete revolution around the sun is called a solar year. On average, a solar year takes 365 days, 5 hours, 48 minutes, and 46 seconds. You could round it and say that the year is 365 days, but that wouldn't make the extra time just go away... The extra time would accumulate, and you'd lose a full day every four years! After a while, the seasons wouldn't match the months. So, to make up for the extra time, we add an extra day to the calendar every four years.

What are the extra days called?

They're called leap days.

What are the years in which the leap days occur called?

They're called leap years.

What was the one exception?

Years ending in "00" would not be leap years anymore, except if they were divisible by 400.

Did the new calendar the Caesar made include leap days every four years?

Yes.