universe summary

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Below is the article summary. For the full article, see universe.

universe, Whole cosmic system of matter and energy of which Earth is a part. Its main constituents are the galaxies, within which are stars and stellar groupings and nebulae (see nebula). Earth’s Sun is one star among the billions of stars in the Milky Way Galaxy. All atoms, subatomic particles, and everything they compose are also part of the universe. The universe is governed by four fundamental forces: the strong force, the weak force, the electromagnetic force, and gravitation. Numerous theories have been proposed for the origin and structure of the universe. See also big bang; cosmology; expanding universe; steady-state theory.

Hubble Space Telescope Summary

Hubble Space Telescope (HST), the first sophisticated optical observatory placed into orbit around Earth. Earth’s atmosphere obscures ground-based astronomers’ view of celestial objects by absorbing or distorting light rays from them. A telescope stationed in outer space is entirely above the

photometry Summary

Photometry, in astronomy, the measurement of the brightness of stars and other celestial objects (nebulae, galaxies, planets, etc.). Such measurements can yield large amounts of information on the objects’ structure, temperature, distance, age, etc. The earliest observations of the apparent

Earth impact hazard Summary

Earth impact hazard, the danger of collision posed by astronomical small bodies whose orbits around the Sun carry them near Earth; when collisions occur, they are known as "impact events." These objects include the rocky asteroids and their larger fragments and the icy nuclei of comets. Space in

Earth Summary

Earth, third planet from the Sun and the fifth largest planet in the solar system in terms of size and mass. Its single most outstanding feature is that its near-surface environments are the only places in the universe known to harbour life. It is designated by the symbol ♁. Earth’s name in