2005/03/11 | 年[Year]
类别(¤〖天文〗) | 评论(0) | 阅读(38) | 发表于 14:11
There are a number of different types of "years" defined for astronomical and civil use. A Gregorian year (or "calendrical year") is the number of days in a given year of the Gregorian calendar (namely, 365 days in non-leap years and 366 days in a leap year ). In the Gregorian calendar , there are 97 leap years out of every 400 years, giving the total number of days in 400 years as

The average number of days in a Gregorian year is therefore

A tropical year is the time from one equinox to the next. A sidereal year is the time between maximum elevation passages of a fixed star. The anomalistic year is the time from one perihelion to the next. The eclipse year is the time from node to node passage of the Moon.

To a layperson, the unqualified term "year" means the number of days in the calendrical year. To an astronomer, however, the unqualified term "year" is generally taken to mean the tropical year,which has length

A mnemonic for the number of seconds in a year is 1 nanocentury is approximately equal to seconds (1 y = s, whereas this approximation gives s).

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