Calendar Origins

The Mayan culture used astronomy to develop their own calendar. Calendars have been around since the beginning of recorded time. That makes sense since calendars are the things that are used to record the passing of days. While the length and structure of calendars change from culture to culture, they all have one basic unit... a day.

The first calendars were based on the phases of the Moon, but the people who developed calendars quickly switched calendars around to be based on the appearance of stars. They didn't immediately understand it was the amount of time it takes for the Earth to revolve around the Sun. Ancient Egyptians saw that certain stars appeared every 365 days. Using that idea, they determined that was one official cycle. That cycle became known as a year.

Different Systems of Measurement

While the Egyptians were advanced in their measurement of time, many other cultures have created calendars. Prehistoric societies were measuring the passage of time with structures that include Stonehenge and other monoliths. Babylonians set up a measurement system based on the phases of the moon with months about 28 days long. They wound up with a calendar that had 354 days in the year.

The Persian calendar is based on observations as opposed to detailed measurements. They still use the Sun to measure years, but its appearance is measure at the vernal equinox (start of spring). Don't think that calendars were limited to the Mediterranean area. The Mayans and other civilizations had developed their own calendars based on the solar and lunar years. The Chinese also developed their own calendar that was based on a solar year, but contained some elements of the lunar year. You may also hear about Chinese years that are associated with animals.

Our Calendar

We use a calendar that is called the Gregorian calendar. The calendar has it's roots in the 300s, but was not refined and used by western nations until 1582. Our modern calendar breaks the year into 365 days and twelve months. Each month has a different number of days ranging from 28 to 31. Every four years, the second month (February) has 29 days to adjust for flaws in the calendar. That special year is called a leap year.

While we measure years with months and days, major solar events still occur at the same time each year. The year starts in winter and the vernal equinox (start of spring) happens on about March 21. The summer solstice (start of summer) happens on about June 21. Fall begins at the autumnal equinox around September 23. Finally, winter begins on about December 21 with the winter solstice. We use the word "around" because the exact exact time that the moments occur changes every year.

Details to Remember

- Our calendar is based on a solar year.
- There are 365 days in a normal year and 366 days in a leap year.
- There are 12 months in a year.
- There are four seasons in a year.

Related Activities

Date and Time Activity Converting Minutes to Hours, Days, and Months
- Play Activity

Date and Time Activity Learn the Names of the Months
- Play Activity


► Or search the sites...

Numbers and Counting

Link to Link to Link to Link to Link to Link to Rader Network Side Navigation

Related Links

Numbernut: Graphs & Grids
Numbernut: Arithmetic Basics
Numbernut: Fractions/Decimals
Biology4Kids: Scientific Method
Biology4Kids: Logic
Chem4Kids: Elements
Fractions Activity

Symbols Activity

NumberNut Sections

Rader's Network of Science and Math Sites