Hodge, Paul Department of Astronomy, University of Washington, Seattle, Washington.
Turner, Edwin L. Princeton University Observatory, Princeton, New Jersey.
Turner, Joyce B. Princeton University Observatory, Princeton, New Jersey.
Last reviewed:January 2019
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- Form and size
- Spiral galaxies
- Elliptical galaxies
- Irregular galaxies
- Exotic galaxy types
- Internal motions
- Clustering and origin of cosmic structure
- Active nuclei
- Links to Primary Literature
- Additional Readings
One of the large self-gravitating aggregates of stars, gas, dust, planets, rocks, and dark matter that occurs by the hundreds of billions in the universe, collectively containing most of the cosmos' visible matter. Everywhere we look beyond our own galaxy into the broader cosmos, the objects we see are, likewise, galaxies (Fig. 1). These “islands in the void” often occur in groups or clusters containing from a few to as many as thousands of individual galaxies, with the clusters ranging from a few hundred thousand to tens of millions of light-years in expanse. See also: Light-year; Matter (physics); Star
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