Calendar

Definition

A calendar is a system for organizing and dividing time, typically defined by the movements of celestial bodies. It includes days, months, and years to track time periods for various activities and events.

5 Must Know Facts For Your Next Test

1. The Gregorian calendar, introduced by Pope Gregory XIII in 1582, is the most widely used civil calendar today.
2. Calendars are based on astronomical cycles such as the Earth's rotation (day), the Moon's phases (month), and Earth's orbit around the Sun (year).
3. Leap years are added to keep calendars in sync with Earth's orbit around the Sun; they include an extra day in February.
4. The lunar calendar is based on the Moon's cycles and has months that are either 29 or 30 days long.
5. Ancient civilizations like the Maya and Egyptians created sophisticated calendars based on their observations of celestial bodies.

Review Questions

• What are the primary celestial cycles that most calendars are based on?
• Why do we have leap years in the Gregorian calendar?
• Name one ancient civilization that developed its own calendar system.

Related terms

Solar Year: The period it takes for Earth to complete one orbit around the Sun, approximately 365.25 days.

Lunar Month: The average time between new moons, approximately 29.5 days.

Leap Year: A year with an extra day added to keep the calendar year synchronized with the astronomical year.