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Photograph of Callisto showing its dark surface heavily cratered with white pock marks.

The Callisto satellite

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Légende : Callisto is the outermost of the four large Galilean moons of Jupiter and the third largest in the whole solar system, falling behind only Ganymede and Saturn's moon Titan. It orbits Jupiter at an average distance of around 1.9 million kilometers, roughly six times the distance between Earth and the Moon. With a diameter of nearly 5,000 kilometers, it is almost as large as Mercury, the smallest planet in our solar system, but has only a third of its mass as it is composed of approximately equal amounts of rock and ice. Callisto orbits Jupiter in a tidally locked rotation, always showing the same side to Jupiter. In contrast to the other three Galilean satellites – Io, Europa, and Ganymede – it is not in orbital resonance due to its farther outward location and is thus not appreciably tidally heated. It does not show any signs of plate tectonics or volcanic activity. Its lack of geological processes means that surface features like craters remain unchanged for billions of years. It is thought to have evolved predominantly under the influence of impacts, as its surface is the oldest and most heavily cratered object in the solar system. In fact, it is so covered in craters that any new impact will likely erase a former one. Callisto's internal structure is still subject to discussion; it may consist of a deep salty ocean. It is thought to be composed mainly of a mix of ice and rock, which are present in various states throughout the inner layers of the moon. Callisto hosts a very thin atmosphere composed mainly of carbon dioxide and some traces of oxygen. The moon has been studied by numerous space probes, such as the Pioneer and Voyager missions and the Galileo orbiter, and will be subject to further explorations by NASA, ESA, and China’s National Space Administration (CNSA).
Crédit : NASA/JPL/DLR
Lien du crédit

Termes du glossaire: Satellites galiléens , Lunes

Licence : Domaine Public Domaine Public Icônes

Fichier ( image 610.45 kB)

Io est peu ou prou sphérique. On y trouve des composés sulfuriques jaunâtres et de petits volcans plus sombres.

Io

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Légende : Le 3 juillet 1999, la sonde spatiale Galileo de la NASA a acquis les images à la plus haute résolution du satellite de Jupiter Io. Io est l'une des quatre lunes joviennes découvertes par Galilée en 1610. Les couleurs de Io témoignent de son importante activité volcanique, car elles proviennent de composés sulfuriques. Les forces de marée de Jupiter et des satellites voisins sont à l'origine du volcanisme de Io.
Crédit : NASA/JPL/Université d'Arizona
Lien du crédit

Termes du glossaire: Satellites galiléens , Io , Lunes
Catégories : Système solaire

Licence : Domaine Public Domaine Public Icônes

Fichier ( image 789.81 kB)

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

vidéo
Créé pour l'OAE

Légende : 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.
Crédit : Ralf Burkart/IAU OAE

Termes du glossaire: Satellites galiléens , Géantes gazeuses , Io , Jupiter , Lunes , Orbite , Planètes extérieures , Planète , Transit
Catégories : Système solaire

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

Ce fichier est sur Zenodo ( vidéo 12.64 MB)

Bright streaks form vertical bars, obscuring the starry sky

Satellite swarm versus night sky beauty, by Torsten Hansen, Germany

image
Créé pour l'OAE

Légende : Third place in the 2021 IAU OAE Astrophotography Contest, category Light pollution. This image of Venus and the Pleiades also shows the tracks of the Starlink satellites. These satellites which are located at an altitude of approximately 550 kilometres, are part of an ever-growing constellation of satellites aimed to provide worldwide internet access. The reflective surfaces of the satellites, coupled with the fact that they are orbiting around the Earth, means that astronomical observations which require very long exposures capture “tracks” of the satellites in their images. Astronomical images used for scientific research are not usable because the measurements and data will contain these “tracks”. Because the number of satellites is expected to grow, it is likely that in the near future there will be no place on Earth where these satellites will not be visible crossing the sky. This is a new type of light pollution that seems to be an upcoming problem we will have to deal with, as these satellites might prevent optimal observation of the sky.
Crédit : Torsten Hansen/IAU OAE

Termes du glossaire: Pollution lumineuse , Satellite artificiel

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

Ce fichier est sur Zenodo ( image 5.66 MB)

Europa est sphérique, de couleurs variant du brun au blanc, couvertes de nombreuses crevasses orientées de façon aléatoire.

Europe

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Légende : Cette image prise par la sonde spatiale Galileo de la NASA en septembre 1996 montre le satellite de Jupiter recouvert de glace, Europe, dans sa couleur naturelle approximative. Les longues lignes sombres représentent des fractures dans la croûte, dont certaines font plus de 3 000 kilomètres de long. L'élément brillant contenant une tache sombre centrale dans le tiers inférieur de l'image est un jeune cratère d'impact d'environ 50 kilomètres de diamètre. Europa a un diamètre d'environ 3 160 km, soit à peu près la taille de la Lune.
Crédit : NASA/JPL/DLR

Termes du glossaire: Satellites galiléens , Lunes
Catégories : Système solaire

Licence : Domaine Public Domaine Public Icônes

Fichier ( image 622.91 kB)

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Le Bureau de l'astronomie pour l'éducation est hébergé par la Maison de l'astronomie sur le campus de l'Institut Max Planck d'astronomie à Heidelberg. Le Bureau de l'astronomie pour l'éducation est un bureau de l'Union Astronomique Internationale, avec un financement important des Fondations Klaus Tschira et Carl Zeiss. Les colloques Shaw-IAU sur l'astronomie pour l'éducation sont financés par la Fondation Shaw Prize.