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Terme du glossaire : Conjonction

Description : Du point de vue d'un observateur sur Terre, lorsque deux objets astronomiques semblent se trouver à proximité dans le ciel, on dit qu'ils sont en conjonction. Il n'est pas nécessaire que la conjonction soit réellement visible - par exemple, la Lune et le Soleil sont approximativement alignés chaque fois qu'il y a une nouvelle Lune, mais nous ne pouvons pas voir la Lune dans ces conditions, à moins qu'il n'y ait une éclipse solaire. Dans ce cas, et lorsqu'une conjonction est si proche qu'un objet semble recouvrir l'autre, les astronomes parlent de transit ou d'éclipse.

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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 ont été aprouvées par un·e spécialiste de la recherche en astronomie et un·e spécialiste de l’éducation

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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Three bright objects in the sky with one top left, one in the middle and one lower centre.

Jupiter, Venus, Moon Conjunction

Légende : Honorable mention in the 2023 IAU OAE Astrophotography Contest, category of Still images taken exclusively with smartphones/mobile devices. Captured with a smartphone in February 2023, over the skies of Luzerne County, Pennsylvania, USA, this photograph offers a glimpse into a conjunction, an enthralling astronomical phenomenon that occurs when two or more celestial objects are seen in close proximity in the sky from our perspective, despite the objects not being physically near to each other. In this image, the brilliance of Jupiter (top), the allure of Venus (middle), and the familiar glow of our Moon (bottom) dance together against a backdrop of delicate clouds and a treeline silhouette, making it a moment worth treasuring.
Crédit : Joslynn Appel/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes


The crescent Moon sits to the left of two bright planets. On the right side the Pleiades star cluster can be seen.

Moon-Mercury-Pleiades Conjunction

Légende : Honourable mention in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This photograph shows the young lunar crescent, some of the nine brightest stars of the Pleiades (with one behind a cloud) on the right, and the planet Mercury, looking slightly red, in the middle of the image. This picture is rather suggestive of the idea that the Pleiades might possibly consist of seven stars. However, the viewer is misled by the clouds; five of the stars form a tiny chariot, one is next to the handle, and three are at the other end of the quadrilateral. Eight stars would be clearly visible if there were no clouds. This configuration of the young Moon next to the Pleiades is visible only in the northern hemisphere spring. Thus it was used by the ancient Babylonians to determine the second month of their year and to judge whether or not an intercalary month was necessary. At least as early as the second millennium before the common era, the Babylonians used several asterisms for each month, with another one of them reappearing every five days after invisibility during daylight. To determine the necessity of intercalation in order to synchronise the solar and the lunar year, the Babylonians used several asterisms, not only the Pleiades. For instance, they also made use of the bright stars Arcturus and Sirius, and they observed a configuration with the Moon as well as heliacal phenomena. The modern Jewish and modern Islamic traditions still make use of some of the Babylonian astronomical rules. However, given that the constellations have shifted as a result of precession, and the fact that nowadays we also have computational means to calculate our calendars, this configuration of the small crescent Moon and the Pleiades is less useful, though it remains exceptionally beautiful. Thus the ancient Babylonian and middle Babylonian tradition survives only rudimentarily. Furthermore, it is unlikely that it is depicted in the Nebra Disc from Bronze Age Europe, as has long been claimed. This image was taken on Elba Island, Italy, in May 2022.
Crédit : Giulio Colombo/ IAU OAE

License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes


The crescent Moon with Venus & Mercury above it in a line in a bright twilight sky above a silhouetted telescope dome

Conjunction of Mercury and Venus above the Moon

Légende : From the observing deck at the European Southern Observatory’s Paranal site in Chile, in March 2008, astronomers captured a conjunction of celestial objects—a moment when two or more astronomical objects appear close together in the sky as seen from Earth. In this scene, the innermost planets Mercury and Venus appear aligned above the Moon, forming a pattern against the sky just before dawn. Although they are at very different distances from Earth, the geometry of their orbits brought them into almost the same line of sight, creating this beautiful cosmic alignment. In the image, the bright crescent Moon is visible low in the sky near the horizon, forming the most prominent object in the lower part of the scene. Just above the Moon, the brighter planet Venus can be seen, while Mercury, fainter and further from the horizon, appears nearby in the upper part of the image.
Crédit : ESO/Y. Beletsky Lien vers les crédits

License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

Diagrammes associés


The Earth's orbit around the Sun with one planet orbiting outside the Earth's orbit and one orbiting inside

Opposition and Conjunction

Légende : This diagram shows the Earth's orbit around the Sun and the orbits of two other planets, one orbiting the Sun outside the Earth's orbit and one orbiting the Sun inside the Earth's orbit. At different times in the orbits of both of these planets, their positions appear to line up with the Earth and the Sun. At these points each planet would appear close to the Sun when viewed from Earth. When this happens each planet is said to be in conjunction with the Sun. For the planet that orbits the Sun within the Earth's orbit it can be in conjunction with the Sun twice in its orbit, once when it is between the Sun and the Earth and once when it is on the other side of the Sun from the Earth. When the planet is in conjunction between the the Sun and Earth it is said to be in inferior conjunction and when it is in conjunction on the far side of the Sun from the Earth it is said to be in superior conjunction. For the planet orbiting the Sun outside the Earth's orbit, it can sometimes be on the other side of the sky. At this point the Earth lies between the planet and the Sun. The planet in this case is said to be in opposition. Opposition and conjunction are not just limited to planets and other types of solar system objects such as dwarf planets, comets and asteroids can also be in opposition and conjunction. However only those objects that have an orbit that takes them outside the Earth's orbit can be in opposition. Conjunction is also used to refer to alignments in the sky between planets in the Solar System. For example when Jupiter and Venus appear very close on the sky when viewed from Earth they are said to be in conjunction with each other.
Crédit : Aneta Margraf/IAU OAE

License: CC-BY-4.0 Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

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