A calendar is an essential organizational tool with many practical applications. Calendars are also important in many religions, marking the religious celebrations and holidays.

The Gregorian Calendar

The yearly calendar we are most familiar with is made up of 12 months:

January, February, March, April, May, June, July, August, September, October, November, and December.

The months are divided into approximately 4 weeks each.

Each week is made up of 7 days:

Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday.

A typical calendar page is shown below.

Notice that in the month shown, there are 31 days. Not all months have 31 days; some months have 30 days. February is a special month that usually has 28 days. However, after every 4 years, February has 29 days!

History of Calendar

The calendar has a long history and many different versions and types of calendars have been invented in the past.

For instance the ancient Egyptians used a calendar based on the sun.

The calendar year consisted of 365 days and it dates back to about 3100 B.C or B.C.E.

Note: B.C stands for Before Christ and B.C.E stands for Before Current Era.

The current calendar is called the Gregorian calendar.

It was invented in 1852 by the Pope at the time, Pope Gregory XIII.

It is based on the sun and the movement of the earth around the sun.

Different Kinds of Calendar

Although the Gregorian calendar is probably the most popular calendar today, there are other calendars that people use.

The Chinese calendar, the Jewish calendar, and the Islamic calendar are 3 of the other calendars that are used today.

A brief description of each calendar is given here :

Chinese Calendar	Jewish Calendar	Islamic Calendar
The Chinese calendar is based on both the sun and the phases of the moon.	The Jewish calendar is based on both the sun and the phases of the moon.	The Islamic calendar is not based on the sun at all, it is based solely on the moon
It has been used since 2637 BCE.	It has been used since 3760 BCE.	It is not calculated exactly.
This calendar has either 12 or 13 months	This calendar also has 12 or 13 months.	The calendar has 12 months, but the beginning of each month is not pre-determined.
The Chinese calendar can have between 353 to 355 days in one year.	It also has 353-355 days (when 12 months) 383-385 days ( when 13 months) in a year.	Islamic year has about 354 days.

Calendar Introduction

A calendar is one of the ways humans have created to mark time.
The calendar most widely used today is called the Gregorian calendar.
The calendar consists of 12 months.
Each month has about 4 weeks and each week has 7 days.
Other calendars in use today include the Chinese calendar, the Jewish calendar, and the Islamic calendar.