Difference between revisions of "Year"
(A '''year''' (from Old English ''gēar'') is the orbital period of the Earth moving around the Sun. For an observer on the Earth, this corresponds to the) |
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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> | ||
Revision as of 14:02, 3 October 2012
A year (from Old English 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.
In astronomy, the Julian year is a unit of time, defined as 365.25 days of Template:Gaps SI seconds each (no leap seconds).[1]
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 annus), in English also y or yr.
Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, hours of daylight, and consequently vegetation and fertility. In temperate and subpolar regions, generally four seasons are recognized: spring, summer, autumn and winter, astronomically marked by the Sun reaching the points of equinox and solstice, although the climatic seasons lag behind their astronomical markers. In some tropical and subtropical regions it is more common to speak of the rainy (or wet, or monsoon) season versus the dry season.
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 years) or 366 (leap years) days.
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".[2]
- ^ International Astronomical Union "SI units" accessed February 18, 2010. (See Table 5 and section 5.15.) Reprinted from George A. Wilkins & IAU Commission 5, "The IAU Style Manual (1989)" (PDF file) in IAU Transactions Vol. XXB
- ^ 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)."
