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ANO (AWN-yoh) Spanish
for year
A calendar year is the time between two dates with the same name in a calendar. Solar calendars usually attempt to predict the four seasons, but because the length of individual seasonal years varies significantly, they instead use an astronomical year as a surrogate. For example, the ancient Egyptians used the heliacal rising of Sirius to predict the flooding of the Nile.
The Gregorian calendar attempts to keep the vernal equinox on or close to March 21; hence it follows the vernal equinox year. The average length of its year is 365.2425 days.
Among solar calendars in wide use today, the Persian calendar is one of the most precise. Rather than being based on numerical rules, the Persian year begins on the day (for the time zone of Tehran) on which the vernal equinox actually falls, as determined by precise astronomical computations.
No astronomical year has an integer number of days or lunar months, so any calendar that follows an astronomical year must have a system of intercalation such as leap years.
In the Julian calendar, the average length of a year was 365.25 days. (This is still used as a convenient time unit in astronomy as shown below.) In a non-leap year, there are 365 days, in a leap year there are 366 days. A leap year occurs every 4 years.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Year".
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