Brenneman, Laura W. High Energy Astrophysics Division, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts.
Behr, Bradford B. Tornado Spectral Systems, Toronto, Canada.
Last reviewed:July 2019
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- Baryonic matter
- Stars and stellar evolution
- Solar system
- Interstellar material
- Groups, clusters, and large-scale structure
- Antimatter (antibaryonic matter)
- Nonbaryonic particles
- Dark matter
- Origin, evolution, and fate
- Big bang
- Cosmological redshifts
- Cosmic background radiation
- Evolution of the universe
- Ultimate fate of the universe
- Additional Readings
Everything in existence, including all matter and energy, and the enormous volume which contains them. The observable universe currently spans about 8.8 × 1023 km (5.5 × 1023 mi), and contains approximately 3.1 × 1054 kg (6.8 × 1054 lb) of matter, yielding an average density equivalent to a few atoms per cubic meter. Most of the universe, then, is empty space; the matter is distributed thinly throughout, forming objects and structures (Fig. 1) at a variety of different sizes. The study of this matter and energy, and its distribution, composition, origin, and evolution, is what constitutes the sciences of astronomy and cosmology. See also: Astronomy; Atom; Cosmology; Density; Energy; Matter
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