Glossary term: Planète

Description: L'Union astronomique internationale définit une planète comme un corps céleste en orbite autour d'une étoile ou d'un vestige d'étoile, qui est suffisamment grand pour être presque sphérique par sa propre force gravitationnelle, mais pas assez massif pour que la fusion thermonucléaire se produise au sein de son noyau. Il doit également être suffisamment massif pour que sa gravité élimine les autres objets qui passent à proximité de son orbite autour de l'étoile. Ce sont donc des corps froids (par rapport aux étoiles) qui ne brillent dans la bande visible que par la lumière réfléchie de leur étoile, mais qui émettent de la lumière dans les longueurs d'onde infrarouges. Dans notre système solaire, huit planètes gravitent autour du Soleil. Les planètes peuvent être essentiellement rocheuses, comme les planètes internes (Mercure, Vénus, Terre et Mars), ou essentiellement liquides et gazeuses avec un petit noyau solide, comme les planètes externes (Jupiter, Saturne, Uranus et Neptune). Les planètes situées en dehors du système solaire sont appelées planètes extrasolaires ou exoplanètes.

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition have been approved by an astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

The planet Jupiter with the two of the four Galilean moons (visible as bright dots) orbiting it.

Jupiter's Rotation, by Vishal Sharma, India

Caption: Third place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons: Jupiter’s Rotation, by Vishal Sharma, India. This time-lapse beautifully shows the rotation of Jupiter and the passage of two Galilean moons on the right side of the frame. Jupiter completes one rotation in just under 10 hours and we see as the Great Red Spot makes its way from left to right. The two moons travel a noticeable fraction of their orbit in this short time. This image was taken in 2020 in the North of India.
Credit: Vishal Sharma/IAU OAE

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

The planet Jupiter, seen here as a bright disk, is orbited by the four Galilean moons, seen here as bright dots

Jupiter Moons Movie2, by Nicolas Hurez, Paul-Antoine Matrangolo, and Carl Pennypacker, United States of America

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This sequence shows the orbit of the four Galilean moons around the planet Jupiter. Almost two entire orbits of the innermost moon, Io, can be seen, with the other moons (Europa and Ganymede, but in particular Callisto) being further away, orbiting noticeably slower. The images were obtained in 2018 with the Las Cumbres Global Observatory at different locations on Earth, allowing a continuous sequence of images over approximately half a week without gaps during the day. With clear skies and over the course of several nights, the motion of the Galilean moons can also be observed with binoculars (ideally steady your elbows on a surface).
Credit: Nicolas Hurez, Paul-Antoine Matrangolo and Carl Pennypacker/IAU OAE

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

Jupiter with coloured horizontal bands of clouds. The shadow of the moon Io is seen as a dark circle in the top left

Jupiter, Io and its shadow, by Ralf Burkart, Germany

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This time-lapse of Jupiter taken in 2017 from Germany beautifully illustrates the transit of one of the Galilean moons, Io, in front of Jupiter. As this is simply a moon casting a shadow on a planet it is equivalent to a lunar eclipse on Earth observed from further away. While the shadow of the moon is clearly visible from the beginning, it might be difficult to spot the moon itself against the background of the beautiful atmospheric bands of Jupiter the first time the video is seen. Watching it repeatedly allows appreciating the rapid motion and rotation in this fantastic observation.
Credit: Ralf Burkart/IAU OAE

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

Mercure

Caption: Cette image est un composite d'une mosaïque d'images de la surface de la planète Mercure obtenues par la sonde spatiale MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging). MESSENGER a été lancée par la NASA en 2004 et a exploré Mercure de 2011 à 2015.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington credit link