Terme du glossaire : Equinoxe
Description : L'équinoxe est le moment de l'année où le Soleil, dans son parcours le long de l'écliptique, traverse l'équateur céleste. Le mot est dérivé du latin aequinoctium avec aequus (égal) et nox, noctis (nuit). Le jour de l'équinoxe, les durées du jour et de la nuit sont à peu près égales sur toute la planète, et non pas seulement près de l'équateur. Pour un observateur terrestre, au cours de cette journée, le Soleil se lève presque exactement à l'Est, se déplace le long de l'équateur céleste et se couche presque exactement à l'Ouest. Il y a deux équinoxes par an, l'un autour du 20 mars et l'autre autour du 23 septembre. Lorsque l'équinoxe a lieu en mars, il indique le passage apparent du Soleil de l'hémisphère Sud vers le hémisphère Nord ; lors de l'équinoxe de septembre, le passage apparent du Soleil se fait du Nord au le Sud.
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Statut du terme et de sa définition : La définition initiale de ce terme en anglais a été aprouvée par un·e spécialiste de la recherche en astronomie et un·e spécialiste de l’éducation La traduction de ce terme et de sa définition n'ont pas encore été aprouvées
Le glossaire multilangue de l'OAE est un projet du Bureau de l'IAU de l'Astronomie pour l'Education (OAE) en collaboration avec le Bureau de l'IAU de diffusion de l'Astronomie (OAO). Les termes et définitions ont été choisis, écrits et relues grâce à un effort collectif de l'OAE, les Centres et les Noeuds de l'OAE, les Coordinateurs Nationaux de l'Astronomie pour l'Education de l'OAE(NAECs) et d'autres volontaires. La liste complète des crédits pour ce projet est disponible ici . Tous les termes du glossaire et leur définition sont déposés sous licence Creative Commons CC BY-4.0 et doivent être créditées au nom de "IAU OAE".
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Dans d'autres langues
- Arabe: الاعتدال
- Allemand: Tagundnachtgleiche
- Anglais: Equinox
- Espagnol: Equinoccio
- Italien: Equinozio
- Japonais: 分点 (Liens externes)
- Portugais brésilien: Equinócio
- Chinois simplifié: 昼夜平分点
- Chinois traditionnel: 晝夜平分點
Media associé
Où le Soleil se couche chaque mois
Légende : Troisième prix du concours d'astrophotographie 2023 de l'UAI OAE, catégorie Images fixes des lieux de lever et de coucher du Soleil au cours de l'année : où le Soleil se couche chaque mois, par John Paul Pile.
Prise avec un smartphone depuis San Rafael, Bulacan, Philippines, cette série d'images a remporté le troisième prix dans la catégorie Images fixes des lieux de lever et de coucher du Soleil au cours de l'année.
Elles montrent l'évolution de la position du coucher du Soleil au cours de l'année en raison de l'inclinaison de l'axe de rotation de la Terre sur le plan de l'écliptique (plan de l'orbite de la Terre autour du Soleil). De janvier à décembre 2022, chaque image reflète l'évolution de la position du Soleil au crépuscule par rapport au même horizon local.
Observez le changement de feuillage et l'apparition d'un poteau électrique en octobre. Cette série d'images est un témoignage visuel de la danse céleste entre la Terre et le Soleil, et des transformations de la nature au fil des saisons.
Crédit : John Paul Pile/UAI OAE (CC BY 4.0)
License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
The Path of the Sun
Légende : Second place winner in the 2023 IAU OAE Astrophotography Contest, category of Still images of day arcs of the Sun and Solargraphs.
This enchanting image, captured in Germany between 21 June 2018 and 21 December 2018, is a poetic blend of art and science, showcasing nature's rhythm and the passage of time. It combines images taken at different times of day over the course of six months. Each curve tracks the Sun’s path (or arc) across the sky on a particular day. The sweeping arc of the Sun is distorted here by the projection, making it appear like a curve. The position of the daily arc across the sky changes with the Sun’s seasonal movement in the sky. Captured using a simple pinhole camera fashioned from a coffee can, it shows the Sun's journey over the course of six months, and the gradual shift of the daily arc from the summer, when it is higher in the sky, to its lowest arc at the winter solstice. Gaps in the Sun’s path represent days or times of day when the Sun was obscured by clouds. This image is a vivid testament to the changing seasons, revealing the Sun's dance in the sky as days grow shorter or longer.
Crédit : Frank Niessen/IAU OAE (CC BY 4.0)
License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Solstices and Equinox
Légende : Honorable mention in the 2023 IAU OAE Astrophotography Contest, category of Still images of day arcs of the Sun and Solargraphs.
This captivating image showcases the journey of the Sun through the sky during the winter solstice (bottom), equinox (middle), and summer solstice (top) in Bursa, Turkey, between 21 December 2007 and 20 June 2008. Using a fisheye lens, the photographer captured the Sun's positions at regular intervals from sunrise to sunset on the three different days, illustrating the changing lengths of day and night throughout the year. The variations in the Sun’s daily path across the sky, its height at midday, and the positions of sunrise and sunset, as well as the length of a day, depend on Earth’s axial tilt relative to its orbit around the Sun. The series was taken from a rooftop in Bursa, where the local terrain adds its own unique touch by occasionally obstructing the horizon. Oriented with north at the top and south at the bottom, this visual diary serves as a stunning representation of the Sun’s path for those residing in mid-northern latitudes.
Crédit : Tunç Tezel/IAU OAE (CC BY 4.0)
License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Occasive Amplitude
Légende : Second place winner in the 2023 IAU OAE Astrophotography Contest, category of Still images of sunrise and sunset location over the year.
Captured from Gatto Corvino village in Sicily, this composite showcases the Sun setting at various points over the sea from the winter to the summer solstice (2016–2017). The centre frame marks due west. As Earth orbits the Sun, the position of the setting (and rising) Sun changes from being northward of due west (east) in summer to southward of due west (east) in winter. During the equinoxes — when day and night are of equal length — the Sun rises directly in the east and sets directly in the west. The changing location of the Sun on the horizon is due to Earth’s axial tilt as it orbits the Sun. In temperate regions of Earth, the Sun’s height above the horizon at noon is at its highest and lowest points in the sky on the summer and winter solstices respectively.
Crédit : Marcella Giulia Pace/IAU OAE (CC BY 4.0)
License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Diagrammes associés
Pisces Constellation Map
Légende : The constellation Pisces along with its bright stars and surrounding constellations. Pisces is surrounded by (going clockwise from the top) Andromeda, Pegasus, Aquarius, Cetus, Aries and Triangulum. Pisces lies on the ecliptic (shown here as a blue line), this is the path the Sun appears to take across the sky over the course of a year. The Sun is in Pisces from mid March to mid April. Thus the Sun is in Pisces at the March equinox. At this point the ecliptic crosses the celestial equator. The Sun’s location at the spring equinox is used to set the zero point of the Right Ascension positional coordinate. The other planets of the Solar System can often be found in Pisces.
Pisces spans the celestial equator and is thus visible at some time in the year from all of planet Earth. In the most arctic or antarctic regions of the world, some parts of the constellation may not be visible. Pisces is most visible in the evenings in the northern hemisphere autumn and southern hemisphere spring
The grand design spiral galaxy M74 is marked on this diagram with a small red circle.
The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope
License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Solstices and Equinoxes
Légende : This diagram demonstrates the relative positions of the Earth and Sun at the two solstices and two equinoxes. The Earth’s rotation axis is tilted by 23.4° from the axis of its orbit. This means that for half the Earth’s annual orbit around the Sun, the Southern Hemisphere is tilted towards the Sun and the Northern Hemisphere is tilted away from the Sun. During this time the Sun appears to lie below the celestial equator. Due to this at any particular point in the Southern Hemisphere the Sun will appear to be higher above the horizon at a particular time of day and the days will be longer. Conversely during this time, the Sun appears lower in the sky at any particular point in the day in the Northern Hemisphere and the days are shorter.
This effect is most pronounced in late December when the Sun appears at its most southerly point in the sky, corresponding to the longest day of the year in the Southern Hemisphere. This normally occurs on the 21st or 22nd of December (UTC), depending on when the most recent leap year was, but can very occasionally occur on the 20th or 23rd of December. This event is known as the December solstice. As the Sun’s rays hit the Southern Hemisphere at a more perpendicular angle during this time, the Southern Hemisphere is typically warmer in this time of year than at other times of year. This is often referred to as summer in temperate and antarctic regions of the Southern Hemisphere and thus the December solstice is known as the summer solstice. South of the Antarctic Circle at this time the Sun never sets and a Polar Day can last several months. Conversely in the Northern Hemisphere, the Sun’s rays hit the Earth at a more grazing angle than at other times of year so it is colder and this solstice is known as the winter solstice. North of the Arctic Circle the Sun never rises during this time and the Polar Night can last several months.
As the year progresses the Earth moves in its orbit and the tilt of the Earth’s axis moves so it appears more side-on to the Sun. From the perspective of an observer on Earth this means that the Sun moves north in the sky, eventually reaching the celestial equator in late March, This usually occurs on the 20th of March (UTC) but can sometimes occur on the 19th or 21st of March. During this time all places on Earth will experience night and day that is approximately 12 hours long. The Sun’s rays now hit the Southern hemisphere at a more shallow angle than they did in December and hit the Northern Hemisphere at a more perpendicular angle. This means that the Northen Hemisphere will have warmed since December and the Southern Hemisphere cooled. This leads to the March equinox being referred to as the autumn equinox in the Southern Hemisphere and the spring or vernal equinox in the Northern Hemisphere.
As the year progresses further the Sun moves further north on the sky, the Northern Hemisphere days lengthen and the Southern Hemisphere days shorten. By June the Earth’s orbit has progressed to the point where the Northern Hemisphere points towards the Sun and the Southern Hemisphere away from the Sun. At one point between the 20th and 22nd of June (UTC) the Sun reaches its most northerly point in the sky, this is known as June solstice. It is now summer in northern temperate and artic regions so this is known as the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere. This is the longest day of the year in the Northern Hemisphere and the shortest day of the year in the Southern Hemisphere. During this time regions north of the Arctic Circle experience a long Polar Day and regions south of the Antarctic Circle experience polar night.
The year progresses further and the Earth moves in its orbit so that the tilt of the Earth’s axis again appears side-on for the Sun. The Sun moves south in the sky and again crosses the celestial equator between the 21st and 24th of September (UTC). At this time all places on the Earth experience equal lengths of day and night. This is known as the September equinox, also called the spring or vernal equinox in the Southern Hemisphere and the autumn equinox in the Northern Hemisphere.
Note the sizes of the Earth, Sun and the Earth’s orbit around the Sun are not to scale in this diagram.
Crédit : Maria Cristina Fortuna/IAU OAE
License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
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