Ekuinoks: Pabidaan ralatan

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(Ma-ulah tungkaran nang isinya ''thumb|The Sun at the moment of the [[March equinox in 2019, when the center of the solar disk contacts the ce...'')
[[File:Sun at moment of spring equinox 2019.jpg|thumb|The Sun at the moment of the [[March equinox]] in 2019, when the center of the solar disk contacts the [[celestial equator]] (the imaginary line on the [[celestial sphere]] above Earth's [[equator]]) from south to north.]]
An '''equinoxEkuinoks''' ismarupakan thefenomena instant of time whenpas [[celestial equator|theekuator planelangit]] oflawan [[Earthekuator]]'s [[equatorbumi]] passesmalewati throughpusat thegeometris geometricmatan center of thecakram [[Sunmatahari]]'s disk.<ref name="USNO FAQ">{{cite web |url=https://aa.usno.navy.mil/faq/docs/equinoxes.php |title=Equinoxes |date=14 June 2019 |work=Astronomical Information Center |publisher=[[United States Naval Observatory]] |archive-url=https://web.archive.org/web/20190525103847/https://aa.usno.navy.mil/faq/docs/equinoxes.php|archive-date=25 May 2019 |url-status=live |access-date=9 July 2019 |quote=On the day of an equinox, the geometric center of the Sun's disk crosses the equator, and this point is above the horizon for 12&nbsp;hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun's disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon. These are the moments of first and last direct sunlight. At these times the center of the disk is below the horizon. Furthermore, atmospheric refraction causes the Sun's disk to appear higher in the sky than it would if the Earth had no atmosphere. Thus, in the morning the upper edge of the disk is visible for several minutes before the geometric edge of the disk reaches the horizon. Similarly, in the evening the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon. The times of sunrise and sunset in almanacs are calculated for the normal atmospheric refraction of 34&nbsp;minutes of arc and a [[semidiameter]] of 16&nbsp;minutes of arc for the disk. Therefore, at the tabulated time the geometric center of the Sun is actually 50&nbsp;minutes of arc below a regular and unobstructed horizon for an observer on the surface of the Earth in a level region}}</ref><ref>{{cite web |url=https://www.esrl.noaa.gov/gmd/grad/solcalc/glossary.html#equinox |title=ESRL Global Monitoring Division - Global Radiation Group |publisher=U.S. Department of Commerce |department=[[NOAA]] |website=www.esrl.noaa.gov |language=EN-US |access-date=9 July 2019}}</ref> ThisFenomena occursngini twicetajadi eachdua yearkali satiap tahunnya, yaitu, aroundpas sakitar [[MarchEkuinoks equinoxMaret|20 MarchMaret]] andwan [[Ekuinoks September equinox|23 September]]. InKawa other wordsdisambat, itbahwa iskajadian thengini momentmarupakan atfenomena whichharatan thetangah centermatahari ofkawa thetaitihi visible Sun isbaandak [[zenithZenit|directlypas abovedi atas ekuator]] the equator.
TheKata wordekuinoks isdiambil derivedmatan from thebasa [[Latin]] ''{{lang|la|aequinoctium}}'', frombaasal matan kata ''{{lang|la|aequus}}'' (equal) and ''{{lang|la|nox}}'' ([[genitive case|genitive]] ''{{lang|la|noctis}}'') (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet. They are not exactly equal, however, due to the [[angular diameter|angular size]] of the Sun, [[atmospheric refraction]], and the rapidly changing duration of the length of day that occurs at most latitudes around the equinoxes. Long before conceiving this equality, primitive equatorial cultures noted the day when the Sun rises due [[east]] and sets due [[west]], and indeed this happens on the day closest to the astronomically defined event. As a consequence, according to a properly constructed and aligned [[sundial]], the daytime duration is 12 hours.
In the [[Northern Hemisphere]], the [[March equinox]] is called the vernal or spring equinox while the [[September equinox]] is called the autumnal or fall equinox. In the [[Southern Hemisphere]], the reverse is true. The dates slightly vary due to [[leap year]]s and other factors.