Years

Years are units of time that are based on the Earth's orbit around the Sun. They are used in many different calendars, including the Gregorian calendar, which is the most widely used civil calendar in the world.

Definition

A year is defined as the period of time it takes for the Earth to complete one orbit around the Sun. This is approximately 365.25 days, which is why most years have 365 days but leap years have 366. The extra day is added to the month of February.

Types of Years

There are several different types of years, including:

• Tropical year: This is the time it takes for the Sun to return to the same position in the cycle of seasons, such as from vernal equinox to vernal equinox. This is the basis for the calendar year.

• Sidereal year: This is the time it takes for the Earth to orbit the Sun once with respect to the fixed stars. It is about 20 minutes longer than the tropical year.

• Anomalistic year: This is the time it takes for the Earth to return to the same point in its elliptical orbit around the Sun. It is about 25 minutes longer than the tropical year.

• Julian year: This is a unit of time used in astronomy, defined as exactly 365.25 days of 86400 SI seconds each, totaling 31557600 seconds.

Use in Calendars

The concept of a year is used in many different calendars, including the Gregorian calendar, the Julian calendar, the Islamic calendar, and the Hebrew calendar. Each of these calendars has a different method for dealing with the fact that a year is not an exact number of days.

See Also

• Month
• Week
• Day
• Hour
• Minute
• Second