Equinox Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! ===General=== Systematically observing the [[sunrise]], people discovered that it occurs between two extreme locations at the [[horizon]] and eventually noted the midpoint between the two. Later it was realized that this happens on a day when the duration of the day and the night are practically equal and the word "equinox" comes from Latin ''aequus'', meaning "equal", and ''nox'', meaning "night". In the northern hemisphere, the ''vernal equinox'' (March) conventionally marks the beginning of [[Spring (season)|spring]] in most cultures and is considered the start of the New Year in the [[Assyrian calendar]], Hindu, and the Persian or [[Iranian calendar]]s,{{efn|The year in the [[Iranian calendar]] begins on [[Nowruz]], which means "new day".}} while the ''autumnal equinox'' (September) marks the beginning of autumn.<ref>{{cite web |url=https://www.timeanddate.com/calendar/march-equinox.html |website=Time and Date |title=March Equinox β Equal Day and Night, Nearly |year=2017 |language=en |access-date=22 May 2017}}</ref> Ancient Greek calendars too had the beginning of the year either at the autumnal or vernal equinox and some at solstices. The [[Antikythera mechanism]] predicts the equinoxes and solstices.<ref>Freeth, T., Bitsakis, Y., Moussas, X., Seiradakis, J. H., Tselikas, A., Mangou, H., ... & Allen, M. (2006). Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism. ''Nature'', ''444''(7119), 587-591.</ref> <gallery widths="200px" heights="160px"> Image:Earth-lighting-equinox_EN.png|Illumination of [[Earth]] by the [[Sun]] at the equinox Image:Ecliptic path.jpg|The relation between the Earth, Sun, and stars at the March equinox. From Earth's perspective, the Sun appears to move along the [[ecliptic]] (red), which is tilted compared to the [[celestial equator]] (white). Image:north season.jpg|Diagram of the Earth's [[season]]s as seen from the north. Far right: December solstice. Image:south season.jpg|Diagram of the Earth's seasons as seen from the south. Far left: June solstice. </gallery> The equinoxes are the only times when the [[terminator (solar)|solar terminator]] (the "edge" between night and day) is perpendicular to the equator. As a result, the northern and southern [[hemispheres of the Earth|hemisphere]]s are equally illuminated. For the same reason, this is also the time when the Sun rises for an observer at one of Earth's rotational poles and sets at the other. For a brief period lasting approximately four days, both North and South Poles are in daylight.{{efn|This is possible because [[atmospheric refraction]] "lofts" the Sun's apparent disk above its true position in the sky.}} For example, in 2021 sunrise on the North Pole is 18 March 07:09 UTC, and sunset on the South Pole is 22 March 13:08 UTC. Also in 2021, sunrise on the South Pole is 20 September 16:08 UTC, and sunset on the North Pole is 24 September 22:30 UTC.<ref>[https://www.timeanddate.com/sun/@90,0 Sunrise and sunset times in 90Β°00'N, 0Β°00'E (North Pole)], timeanddate.com</ref><ref>[https://www.timeanddate.com/sun/@-90,0 Sunrise and sunset times in 90Β°00'S, 0Β°00'E (South Pole)], timeanddate.com</ref> In other words, the equinoxes are the only times when the [[subsolar point]] is on the equator, meaning that the Sun is [[Zenith|exactly overhead]] at a point on the equatorial line. The subsolar point crosses the equator moving northward at the March equinox and southward at the September equinox. Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page