Brenneman, Laura W. High Energy Astrophysics Division, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts.
Behr, Bradford B. Tornado Spectral Systems, Toronto, Canada.
- Baryonic matter
- Stars and stellar evolution
- Solar system
- Extrasolar planets
- Interstellar material
- Groups, clusters, and large-scale structure
- Nonbaryonic particles
- Dark matter
- Origin, Evolution, and Fate
- Big bang
- Cosmological redshifts
- Cosmic background radiation
- Evolution of the universe
- Ultimate fate of the universe
- Links to Primary Literature
- Additional Readings
The universe comprises 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 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.
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