Glossary term: Milky Way


The Milky Way is our galaxy. It is an aggregate of about 100–400 billion stars. Our Solar System is located about 26,600 light years from the center of the Milky Way. In the night sky we can see it as a faint band extending across the sky with its center in the Sagittarius constellation. The Milky Way is a relatively large spiral galaxy, and the distribution of stars in it extends to about 100,000 light years along the disk with a thickness of about 1000 light years. This disk is surrounded by a much more sparse halo of stars. In addition to stars, the Milky Way is comprised of interstellar medium and dark matter. While the interstellar medium is limited mostly to the disk, the surrounding dark matter halo extends to much larger distances. The center of the Milky Way hosts a supermassive black hole which is about 4 million times the mass of the Sun.

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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".

Related Media

The Milky Way as a bright band over the horizon. The right of the image shows structure of light and dark patches in the band

Milky Way Arch over Lut Desert, Iran, by Amirreza Kamkar, Iran (Islamic Republic of)

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Wide star fields. This panoramic dawn image shows the majestic band of the Milky Way – our home Galaxy – made up of a few hundred billion stars, among other structures, most of which are not detectable by our eyes, or in some cases even directly with telescopes. The appearance of the band is because the Milky Way is a disc-shaped galaxy, and we (Earth/Solar System) are situated within the disc. Diverse cultures and traditions around the world each have their own name and cultural stories for the Milky Way. The dark regions visible in the Milky Way are large, dense, cool nebulae (clouds of dust and gas), which obscure the light from stars in the Milky Way. The Indigenous Australians associate stories with the dark patches of the Milky Way, one of the most prominent being the Emu in the Sky (called Tchingal in Wotjobaluk country). In and around the band of the Milky Way there are a vast range of star clusters, two familiar ones are M6 (Butterfly cluster) and M7 (Ptolemy’s cluster). The bright point just above the horizon is the planet Venus (known to the Boorong people of Indigenous Australia as Chargee Gnowee, elder sister of the Sun). Within the band of the Milky Way the brightest point in the image is the planet Jupiter (called Ginabongbearp, the Sulphur-crested white cockatoo by the Boorong). The planet Saturn is the bright point between Venus and Jupiter (closer to Venus than Jupiter). There are two constellations and one asterism that can be easily discerned in the image: Aquila, Scorpio (Maui’s Hook), and Teapot (asterism in Sagittarius). In this image, the center of the Milky Way at an approximate distance of 26,000 light years from Earth, is located roughly to the top right of the Teapot spout. The bright red-orange point to the right of Jupiter is the red supergiant star Antares and is part of the constellation Scorpio (known as Maui’s Hook in Māori and Polynesian cultures). This variation in the colour of stars is the result of temperature of the stars (lower temperature stars are redder, higher temperatures stars are bluer).
Credit: Amirreza Kamkar/IAU OAE
License: CC-BY-4.0 Creative Comments Attribution 4.0 International (CC BY 4.0) icons