Astrophysics (Encyclopedia of Science)
Astrophysics uses the already understood theories of physics (the study of matter and energy) to describe astronomical (universal) phenomena or events. Astrophysicists try to understand the processes that cause our universe and everything in it to behave the way it does.
For thousands of years, humans observed phenomena in the sky, but had no physical explanation for what they saw. Scientists in the twentieth century, however, have been able to explain many astronomical phenomena in terms of detailed physical theories, relating them to the same chemistry and physics at work in our everyday lives.
Whereas experiments in many other scientific fields can be performed under controlled conditions in a laboratory, astrophysical experiments cannot: the energies and distances involved are simply too great. Even though conditions vary greatly throughout the universe, astrophysicists can observe events in the sky and then develop theories about those events based on the laws that govern our day-to-day experiences on Earth. It is common belief that the laws of physics are consistent throughout the universe.
Processes in the universe
The first astrophysical concept or law to be recognized was the law of gravity. Although it is a very weak force compared to the other fundamental forces of...
(The entire section is 449 words.)
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Astrophysics (Encyclopedia of Science and Religion)
Astrophysics is the analysis of the physical structure and evolution of objects studied by means of astronomical observations (e.g., stars, galaxies, radio sources, X-ray sources, quasi-stellar objects). The physical structure of such objects depends on a balance of gravitation, radiation pressure, and centrifugal forces, while their evolution depends on their initial composition and the reactions that take place between matter and radiation. In particular, nuclear reactions create new elements in the interior of stars and provide their major energy source. Detailed analysis discloses important relations between the color of light emitted by a star and its total radiation output; this relation changes with the age of the star. At its life's end, a star may die in a supernova explosion, or it may end up as a white dwarf star, neutron star, or black hole, depending on its mass.
See also ASTRONOMY; BLACK HOLE; COSMOLOGY, PHYSICAL ASPECTS; GRAVITATION
GEORGE F. R. ELLIS