A year is divided into 12 months in the modern-day Gregorian calendar. The months are either 28, 29, 30, or 31 days long.
The Gregorian calendar is divided into 12 months. Each month has either 28, 30, or 31 days during a common year, which has 365 days. During leap years, which occur nearly every 4 years, we add an extra (intercalary) day, Leap Day, on 29 February, making leap years 366 days long. This is to keep our current calendar aligned with the solar year and astronomical seasons marked by equinoxes and solstices. Go to calendar
The 12 Months:
The Gregorian calendar consists of the following 12 months:
- January - 31 days
- February - 28 days in a common year and 29 days in leap years
- March - 31 days
- April - 30 days
- May- 31 days
- June- 30 days
- July- 31 days
- August - 31 days
- September - 30 days
- October- 31 days
- November - 30 days
- December - 31 days
The Romans named some of the months after their position in the calendar year: September means the 7th month, October the 8th, November the 9th, and December the 10th month. However, when January and February were eventually added and the beginning of the calendar year was moved to January, the position of these months no longer corresponded with the original meaning of their names.
Today, we still call the 9th month of the year September, the 7th month. The Islamic calendar, the Hebrew calendar, and the Hindu calendar also use months to divide up the year. Although the Gregorian calendar is the most commonly used calendar today, other calendars are still used in many parts of the world to calculate certain holidays and annual feasts.
What is a month?
A month is a collection of approximately 30 days. Months were originally chosen from the period of time it takes for the Moon to orbit the earth. There are 12 months in a year. The moon takes about 29.5 days to fully orbit the earth. Therefore we chose about 30 days for each month.
January is the first month of the year and January 1st is known as new year’s day. December is the final month of the year and December 31st is known as new year’s eve. At midnight on December 31st the year ends and a new year begins on January 1st. You can remember how many days in each month using this rhyme:
January
Jan 31
2
February
Feb 28 (29 in leap years)
3
March
Mar 31
4
April
Apr 30
5
May
May 31
6
June
Jun 30
7
July
Jul 31
8
August
Aug 31
9
September
Sep 30
10
October
Oct 31
11
November
Nov 30
12
December
Dec 31
The Moon:
The months were originally based on the movement of the moon (the words moon and month are related), but this did not work out perfectly for one year.
So they changed how many days in some months to make them all add up to one year.
Ancient Romans had 10 Months:
- Martius for the god Mars
- Aprilis (the period is Latin for “open”, and flowers blossom in this month)
- Maius for the goddess Maia
- Iunius for the goddess Juno
- Quintilis from Latin meaning five
- Sextilis for six
- Septembris for seven
- Octobris for eight
- Novembris for nine
- Decembris for ten (remember “Decimal” means based on 10)
Then around 710 BC Numa Pompilius, the second King of Rome,
| month | short form | days | season | |
|---|---|---|---|---|
| 1 | January | Jan. | 31 | winter |
| 2 | February | Feb. | 28/29 | |
| 3 | March | Mar. | 31 | spring |
| 4 | April | Apr. | 30 | |
| 5 | May | May | 31 | |
| 6 | June | Jun. | 30 | summer |
| 7 | July | Jul. | 31 | |
| 8 | August | Aug. | 31 | |
| 9 | September | Sep. | 30 | autumn |
| 10 | October | Oct. | 31 | |
| 11 | November | Nov. | 30 | |
| 12 | December | Dec. | 31 | winter |
| The seasons are approximate and depend on latitude. Some parts of the world have only three seasons. The seasons shown here are for the North Temperate Zone (for example North America). In the southern hemisphere, the seasons are reversed. |