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− | '''Year''' | + | A '''year''' (from [[Old English language|Old English]] ''[[Jēram|gēar]]'') is the [[orbital period]] of the [[Earth]] moving around the [[Sun]]. For an observer on the Earth, this corresponds to the period it takes the Sun to complete one course throughout the [[zodiac]] along the [[ecliptic]]. |
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| + | In astronomy, the [[Julian year (astronomy)|Julian year]] is a [[unit of time]], defined as 365.25 [[day]]s of {{gaps|86|400}} [[second|SI second]]s each (no [[leap second]]s).<ref>[[International Astronomical Union]] "[http://www.iau.org/science/publications/proceedings_rules/units/ SI units]" accessed February 18, 2010. (See Table 5 and section 5.15.) Reprinted from George A. Wilkins & IAU Commission 5, [http://www.iau.org/static/publications/stylemanual1989.pdf "The IAU Style Manual (1989)"] (PDF file) in ''[[IAU Transactions]]'' Vol. XXB</ref> |
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| + | There is no universally accepted symbol for the year as a unit of time. The [[International System of Units]] does not propose one. A common abbreviation in international use is '''a''' (for Latin ''[[:wikt:annus|annus]]''), in English also '''y''' or '''yr'''. |
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| + | Due to the Earth's [[axial tilt]], the course of a year sees the passing of the [[season]]s, marked by changes in [[weather]], hours of [[daylight]], and consequently [[vegetation]] and [[Fertility (soil)|fertility]]. |
| + | In [[temperate]] and [[Subpolar climate|subpolar]] regions, generally four seasons are recognized: ''[[Spring (season)|spring]]'', ''[[summer]]'', ''[[autumn]]'' and ''[[winter]]'', astronomically marked by the Sun reaching the points of [[equinox]] and [[solstice]], although the climatic seasons [[Seasonal lag|lag behind]] their astronomical markers. |
| + | In some [[tropics|tropical]] and [[subtropical]] regions it is more common to speak of the [[wet season|rainy]] (or wet, or [[monsoon]]) season versus the [[dry season]]. |
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| + | A [[calendar year]] is an approximation of the Earth's orbital period in a given [[calendar]]. |
| + | A calendar year in the [[Gregorian calendar]] (as well as in the [[Julian calendar]]) has either 365 ([[common year]]s) or 366 ([[leap year]]s) days. |
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| + | The word "year" is also used of periods loosely associated but not strictly identical with either the astronomical or the calendar year, such as the [[seasonal year]], the [[fiscal year]] or the [[academic year]], etc. |
| + | By extension, the term ''year'' can mean the orbital period of any [[planet]]: for example, a "Martian year" is the time in which Mars completes its own orbit. The term is also applied more broadly to any long period or cycle, such as the "[[Great Year]]".<ref>[[OED]], s.v. "year", entry 2.b.: "''transf.'' Applied to a very long period or cycle (in chronology or mythology, or vaguely in poetic use)."</ref> |