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Terme du glossaire : Galaxie spirale

Description : Les galaxies spirales sont des galaxies qui possèdent des bras spiraux : des régions de plus forte densité qui se forment lors de la rotation d'une galaxie, où le gaz et la poussière sont comprimés et où de nouvelles étoiles naissent. La plupart des galaxies spirales sont des galaxies à disque, c'est pourquoi les deux noms sont parfois utilisés de manière interchangeable. La plupart des galaxies spirales ont un bulbe central d'étoiles, et beaucoup (y compris la Voie lactée) ont une barre centrale. Les galaxies spirales se distinguent des galaxies elliptiques, lenticulaires, irrégulières et naines (bien qu'il existe également des galaxies spirales naines).

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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".

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Deux galaxies spirales s'embrassant aux premiers stades de leur fusion, avec des distorsions visibles sur la plus petite galaxie.

Fusion de galaxies spirales

Légende : Cette image montre deux galaxies spirales en interaction, situées à environ 150 millions d'années-lumière. Deux galaxies spirales sont impliquées dans cette danse, créant des distorsions visibles dans leurs bras spiraux en raison de l'attraction gravitationnelle. Ce qui commence comme une étreinte sur cette image se terminera par la fusion de ces deux galaxies en une seule galaxie, très probablement elliptique.
Crédit : ESO Lien vers les crédits

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


Andromeda is a bright disk, with dark spiral lines in it, tilted up at the west end. Two small bright blobs lie left & right

A visible light image of the Andromeda Galaxy

Légende : The Andromeda Galaxy viewed in visible light. Like our Milky Way, Andromeda is a barred spiral galaxy. Here we can see its bright core and spiral disk. The glow from the stars in the disk is interrupted by lanes of dust that form part of its spiral structure. Andromeda is the largest galaxy in the Local Group of galaxies that includes the Milky Way. To the left of the core and just above the disk we see the dwarf galaxy M32 and to the right and below the disk we see the dwarf galaxy M110. These are both satellite galaxies of the Andromeda Galaxy.
Crédit : Torben Hansen Lien vers les crédits

License: CC-BY-2.0 Creative Commons (CC) Attribution 2.0 Générique Icônes

Diagrammes associés


Leo resembles a lion standing on the ecliptic (which runs ESE to WNW) with its nose pointed northwest.

Leo Constellation Map

Légende : The zodiac constellation Leo and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Leo Minor, Cancer, Sextans, Hydra, Crater, Virgo and Ursa Major. The brightest star in Leo, Regulus, lies almost exactly on the ecliptic (shown here as a blue line): the path the Sun appears to take across the sky over the course of a year. The Sun spends the period from mid August to mid September in Leo. The other planets in the Solar System can often be found in Leo. Leo spans the celestial equator and is thus part of it is visible at some time in the year from all of planet Earth with some of the constellation obscured for the most arctic and antarctic regions of the world. Leo is most visible in the evenings in the northern hemisphere spring and southern hemisphere autumn. Several objects can be seen in Leo, including M65 and M66 – two galaxies in the Leo Triplet, a trio of galaxies including NGC 3628, not listed here. In addition, M96, a spiral galaxy, can be seen as a fuzzy object using a small telescope, and Messier 105, an elliptical galaxy. Each of these objects are labelled on the map as red ellipses. 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 labelled 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


The constellation Virgo appears as a person lying with their back roughly against the diagonal ecliptic, arms outstretched, and feet pointed east.

Virgo Constellation Map

Légende : The zodiac constellation Virgo and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Coma Berenices, Leo, Crater, Corvus, Libra, and Bootes. The brightest star in Virgo, Spica, lies just below the ecliptic (shown here as a blue line) in the middle of the map. One way of locating this star in the night sky is to follow the handle of the Big Dipper to the star Arcturus in Bootes and go along a line straight down to Spica (“arc to Arcturus and spike to Spica”). This star lies just below the ecliptic. The ecliptic is the path the Sun appears to take across the sky over the course of a year. The Sun is in Virgo from mid September to late October. The other planets of the Solar System can often be found in Virgo. Virgo spans the celestial equator and is thus part of it is visible at some time in the year from all of planet Earth with some of the constellation obscured for the most arctic and antarctic regions of the world. Virgo is most visible in the evenings in the northern hemisphere spring and southern hemisphere autumn. The constellation Virgo appears as a person lying with their back roughly against the ecliptic, arms outstretched, and feet pointed east. Several deep-sky objects are visible in Virgo, including NGC4697, M49, M87, M86, M84, and M60, all of which are labelled as red ellipses on the map. These are all spiral and elliptical galaxies located several millions of lightyears from Earth. Most notably, M87 is host to the supermassive black hole (Pōwehi) that was imaged by the Event Horizon Telescope in 2019. All of these galaxies are members of the Virgo Cluster, the nearest cluster of galaxies to the Milky Way. 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 labelled 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


La Grande Ourse apparaît comme une louche avec le manche à l'est et la coupe à l'ouest. Des lignes d'étoiles plus faibles s'étendent vers le sud.

Carte de la constellation LA GRANDE OURSE

Légende : La constellation de la Grande Ourse avec ses étoiles brillantes et les constellations qui l'entourent. La Grande Ourse ou Ursa Major est entourée de (dans le sens des aiguilles d'une montre à partir du haut) : Dragon, Caméléon, Lynx, Petit Lion, Lion, Chevelure de Bérénice, Chiens de Chasse et Bouvier. La Grande Ourse est célèbre pour son astérisme proéminent, souvent connu en anglais sous le nom de Big Dipper ou the Plough (la Grande Ourse ou la Charrue). Cet astérisme nordique proéminent porte une grande variété de noms dans les cultures du monde entier. Alors que la plupart des constellations et des astérismes sont constitués d'étoiles sans rapport les unes avec les autres qui apparaissent au hasard dans le ciel, cinq des étoiles de la Grande Ourse font partie du groupe mobile de la Grande Ourse, un groupe d'étoiles qui se déplacent ensemble dans l'espace et qui se sont probablement formées au même endroit il y a 300 millions d'années. Les deux étoiles situées à l'extrémité droite de la Grande Ourse sur ce diagramme forment une paire d'étoiles indicatrices qui peuvent être utilisées pour localiser Polaris, l'étoile du pôle nord qui se trouve dans la constellation de la Petite Ourse. La Grande Ourse est une constellation septentrionale, visible depuis les régions septentrionales et équatoriales. Certaines parties de la constellation sont visibles depuis toutes les régions de l'hémisphère sud, à l'exception des régions les plus antarctiques, mais toutes les régions tempérées de l'hémisphère sud ne peuvent pas voir l'intégralité de la Grande Ourse. Inversement, la Grande Ourse et une grande partie du reste de la constellation sont circumpolaires dans les régions arctiques et dans de nombreuses régions tempérées de l'hémisphère nord. La Grande Ourse est surtout visible le soir au printemps dans l'hémisphère nord et en automne dans l'hémisphère sud. Deux galaxies importantes apparaissent dans la partie nord de cette constellation, la galaxie spirale M81 et M82, une galaxie spirale possible dont la structure est difficile à observer depuis la Terre car elle apparaît sur le bord. Ces deux galaxies sont représentées ici par des ellipses rouges. La nébuleuse planétaire M97 (la nébuleuse du Hibou) se trouve au milieu de la constellation et est marquée par un cercle vert superposé à un symbole plus. L'axe des y de ce diagramme est en degrés de déclinaison avec le nord en haut et l'axe des x est en heures d'ascension droite avec l'est à gauche. La taille des étoiles marquées ici correspond à la magnitude apparente de l'étoile, une mesure de sa luminosité apparente. Les points les plus gros représentent les étoiles les plus brillantes. Les lettres grecques indiquent les étoiles les plus brillantes de la constellation. Elles sont classées par ordre de luminosité, l'étoile la plus brillante étant étiquetée alpha, la deuxième plus brillante bêta, etc., bien que cet ordre ne soit pas toujours respecté à la lettre. Les lignes pointillées marquent les limites des constellations selon l'UAI et les lignes vertes pleines marquent l'une des formes couramment utilisées pour représenter les figures des constellations. Ni les limites des constellations, ni les lignes reliant les étoiles n'apparaissent sur le ciel.
Crédit : Adapté par le Bureau de l'astronomie pour l'éducation de l'AIU à partir de l'original de l'AIU/Sky & Telescope

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


Camelopardalis has no very bright stars and no well-defined shape

Camelopardalis Constellation Map

Légende : The constellation Camelopardalis with its bright stars and surrounding constellations. Camelopardalis is surrounded by (going clockwise from the top): Cepheus, Cassiopea, Perseus, Auriga, Lynx, Ursa Major, Draco and Ursa Minor. Camelopardalis is a large constellation but contains relatively few bright stars. Camelopardalis is a northern constellation and as such the whole constellation is visible for the whole northern hemisphere at some point in the year. It is also visible from equatorial parts of the southern hemisphere with some parts visible to temperate southern regions. The whole constellation is circumpolar for all arctic and more northerly temperate regions of the northern hemisphere. Camelopardalis is best viewed in the evening in the late northern hemisphere winter and late southern hemisphere summer. The spiral galaxies NGC 2403 and IC 342 lie in Camelopardalis and are marked here with red ellipses. This diagram maps an area around the north celestial pole. Here lines of constant right ascension converge. The right ascension values of these lines are marked on the x-axis above and below the diagram. Some of the lines of constant declination are marked on the y-axis. 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 lines joining the stars appear on the sky.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope

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


Cepheus appears as a head wearing a pointy hat tilted anticlockwise by 45 degrees

Cepheus Constellation Map

Légende : The constellation Cepheus along with its bright stars and surrounding constellations. Cepheus is surrounded by (going clockwise from the top): Camelopardalis, Ursa Minor, Draco, Cygnus, Lacerta and Cassiopeia. Cepheus is a large constellation. Its most notable star is Delta Cephei, the prototype for the class of variable stars known as Cepheid variables. These are variable stars which can be used to estimate distances both within our galaxy and to nearby galaxies. Cepheus lies close to the north celestial pole. As such it is circumpolar for arctic and temperate regions of the northern hemisphere. The whole of the constellation is also visible at some point in the year in equatorial regions of the northern hemisphere with parts of it visible in equatorial regions of the southern hemisphere. It is best viewed in the evening in the northern hemisphere late autumn and southern hemisphere late spring. The open cluster NGC 188 lies in Cepheus and is marked here with a yellow circle. The nebula NGC 7023 also lies in the constellation and is marked with a green square. The red ellipse in the lower right marks the position of the spiral galaxy NGC 6946. This diagram maps an area around the north celestial pole. Here lines of constant right ascension converge. The right ascension values of these lines are marked on the x-axis above and below the diagram. Some of the lines of constant declination are marked on the y-axis. 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. Delta Cephei is marked with a circle around a dot as it is a variable star. Mu Cephei is also a variable star marked here as an open circle. 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 lines joining the stars appear on the sky.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope

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

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