Star cloud

(astronomy) An aggregation of thousands or of millions of stars spread over hundreds or thousands of light-years.

Large groupings of stars with dimensions of 1000 to several thousand light-years. Star clouds are not stable clusterings of stars or even groups of a common origin, such as stellar associations. Instead, they are large areas where the stellar density is higher than average in a galaxy. They are nevertheless physical entities in that they result from large-scale star formation events or series of events that are to some extent limited in size by the characteristics of the galactic environment.

Large star clouds are found commonly in the spiral arms of galaxies such as the Milky Way Galaxy and the Andromeda Galaxy (M31), but are not found in smaller, dwarf galaxies or in very old galaxies. Conspicuous star clouds in the Milky Way Galaxy are found in the constellations Carina, Cygnus, Sagittarius, and Scutum. See also Andromeda Galaxy; Milky Way Galaxy; Star.

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Sagittarius Star Cloud

A star cloud is a group of stars that appear to be in the same position in the sky. These are not true star clusters, but rather dependent on the point of view of the observer. The stars that make up the cloud do not actually reside close to each other, they are just in the same line-of-sight.

See also

• Multiply imaged quasar
• Double star
• Constellation
• Nebula
• Cloud

v • d • e Stellar systems Bound Galaxy · Dwarf galaxy · Globular cluster · Open cluster · Binary star · Multiple star system Unbound Stellar stream · Stellar association · Moving group · Runaway star · Hypervelocity star Visual grouping Double star · Multiple star · Constellation · Asterism · Star cloud

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