Year

Definition

A year is the period of time it takes for a planet to complete one orbit around its star. On Earth, a year is approximately 365.25 days long.

5 Must Know Facts For Your Next Test

1. A tropical year on Earth is about 365.24 days and is used to keep our calendar in alignment with the Earth's seasons.
2. The concept of a year varies depending on the celestial body being observed; for example, a Martian year is about 687 Earth days.
3. Ancient astronomers used observations of the sky to develop early calendars based on the solar year.
4. The Gregorian calendar, which we use today, accounts for leap years to correct for the extra 0.25 day each year.
5. Understanding the length of a year on different planets helps astronomers study their climates and seasonal changes.

Review Questions

• What is a tropical year and how does it differ from a calendar year?
• How did ancient astronomers use their observations of the sky to develop early calendars?
• Why are leap years included in the Gregorian calendar?

Related terms

Astronomical Unit (AU): A unit of measurement equal to the average distance between Earth and the Sun, approximately 93 million miles.

Leap Year: A year containing an extra day (February 29) to keep the calendar year synchronized with the astronomical or seasonal year.

Sidereal Year: The time taken by Earth to orbit once around the Sun relative to fixed stars, roughly 365.25636 days.