Glossary term: Andromeda Galaxy

Description: The Andromeda galaxy is a spiral galaxy like ours although twice as large. It is the only such galaxy visible to the naked eye from the northern hemisphere, although only from dark places away from city light. It is also known as M31 after the French astronomer Charles Messier, who created a catalog of 110 objects with Andromeda in position 31.

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Term and definition status: This term and its definition have been approved by a research 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".

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The bright, diffuse Milky Way, interrupted by mottled dark patches, arches over a wintry landscape.

Winter Milky Way

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   Taken near Lake Misurina in the Veneto region of Italy in February 2019, this image shows a clear and starry sky over a winter landscape. We can see part of the Milky Way arc. From the left side, towards the south-east, we see Sirius, "The Burner" in Greek, the brightest star in the night sky. It is part of the constellation Canis Major, The Great Dog, one of the dogs of Orion, the great hunter, in Greek mythology. Orion’s other dog, Canis Minor, the Small Dog, is represented by the bright star Procyon and its fainter neighbours. The Greek star name means “The One [rising] before The Dog” and the star is seen at the top left side of the image just above the arc of the Galaxy. Orion lies to the right of Canis Major. We can spot its characteristic “belt”, an asterism composed of three bright stars aligned in a straight line.  Above the treetops to the right of Orion, the open star clusters of the Hyades and the Pleiades in the constellation Taurus, the Bull, are visible. According to ancient lore, these two clusters form a Celestial Gate directly next to the intersection of the great circles of the ecliptic and the Milky Way. In Greco-Roman mythology, Taurus is associated with the god Zeus who is said to have used a bull to seduce the Phoenician princess Europa. Above the constellation Taurus, we can see a bright star just above the arc of the Galaxy. This is Capella, the brightest star of the constellation Auriga, The Charioteer. This is one of the 88 modern constellations and is associated with the Greek hero Erichthonius of Athens. Hindu astronomy considers Capella as the heart of Brahma, one of the three major gods. The indigenous people of Bororo in Brazil have a constellation representing a cayman, comprising some of the stars of Auriga and some stars from neighbouring constellations. To the right of Taurus, we find the modern constellation Perseus with the bright double star cluster h+chi Perseii, which represents the metal of Perseus’s sabre in Greek mythology. Perseus is the hero who was sent out to prove himself, and happened to rescue Andromeda from the sea monster Cetus as the Roman poet Ovid wrote. We can also see the constellation Cassiopeia, associated with the queen and mother of Andromeda in Greek mythology. It is composed of five bright stars in the shape of a W, which was considered the asterism of The Key by the Greeks according to the poet Aratus. The recognisable shape is also associated with other mythologies: for instance, it represents the princess Sharmishtha in Hindu astronomy, a bat in Thailand, and a camel in native Arabic astronomy. In the gap between the trees, the Andromeda Galaxy is visible.
Credit: Giorgia Hofer/IAU OAE

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