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The 12 Months of the Year

A year is divided into 12 months in the modern-day Gregorian calendar.

Illustration image

Calendar with 12 months.

The Gregorian calendar is divided into 12 irregular 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.

The 12 Months

The Gregorian calendar consists of the following 12 months:

  1. January - 31 days
  2. February - 28 days in a common year and 29 days in leap years
  3. March - 31 days
  4. April - 30 days
  5. May - 31 days
  6. June - 30 days
  7. July - 31 days
  8. August - 31 days
  9. September - 30 days
  10. October - 31 days
  11. November - 30 days
  12. December - 31 days

Tracking the Moon's Orbit

The months originated as a way to mark time and break up the year into shorter periods based on the Moon’s orbit around Earth. The word month is even derived from the word Moon.

As far as we know, months were first used in Mesopotamia sometime between the years 500 BCE and 400 BCE to measure the natural period related to the lunar month, or synodic month, which is the time it takes for the Moon to go through all the Moon phases.

How Many Have 28, 29, 30, or 31 Days?

The Gregorian calendar has 4 months that are 30 days long and 7 months that are 31 days long. February is the only month that is 28 days long in common years and 29 days long in leap years.

From 10 to 12 Months

Our current Gregorian calendar and its predecessor, the Julian calendar, both have 12 months. The even earlier Roman calendar also had 12 months, however, only 10 of the months had names.

The addition of January and February moved the months September, October, November, and December to later in the year so they no longer correspond with the original meaning of their names. In the Roman calendar, their original names in Latin mean theseventh, eighth, ninth, and tenth month.

There are many calendars that still use months to divide up the year. The Islamic calendar, the Hebrew calendar, and the Hindu calendar are a few examples. Although the Gregorian calendar is the most commonly used calendar today, other calendars are still used to calculate certain holidays and annual feasts to correspond with the Gregorian calendar.

Old Names of Months

Months in the ancient Roman calendar include:

  • Mercedonius - an occasional month after February that would be used to realign the Roman calendar. Today we use Leap Day for this alignment.
  • Quintilis - renamed July in honor of Julius Caesar in 44 BCE.
  • Sextilis - renamed August in honor of Roman Emperor Augustus in 8 BCE.

Topics: January, February, March, April, May, June, July, August, September, October, November, December, Months

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Calendar Types

  1. Gregorian Calendar
  2. Julian Calendar
  3. Revised Julian Calendar
  4. Islamic Calendar
  5. Jewish Calendar
  6. Persian Calendar
  7. Mayan Calendar
  8. Chinese Calendar
  9. Roman Calendar
  10. Ethiopian Calendar
  11. Switch from Julian to Gregorian
  12. Is There a Perfect Calendar?
  13. What Do CE and BCE Mean?

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