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Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, Astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space–what they are, rather than where they are." Among the subjects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
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The discovery of cosmic microwave background radiation constitutes a major development in modern physical cosmology. In 1964, US physicist Arno Allan Penzias and radio-astronomer Robert Woodrow Wilson discovered the CMB, estimating its temperature as 3.5 K, as they experimented with the Holmdel Horn Antenna. The new measurements were accepted as important evidence for a hot early Universe and as evidence against the rival steady state theory as theoretical work around 1950 showed the need for a CMB for consistency with the simplest relativistic universe models. In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint measurement. There had been a prior measurement of the cosmic background radiation (CMB) by Andrew McKellar in 1941 at an effective temperature of 2.3 K using CN stellar absorption lines observed by W. S. Adams. Although no reference to the CMB is made by McKellar, it was not until much later after the Penzias and Wilson measurements that the significance of this measurement was understood.
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.
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References
- 1 2 "John Ruhl, Connecticut Professor". Physics faculty. Case Western Reserve University. Retrieved 2023-08-16.
- ↑ Holstein, Barry R. (May 1992). "Review of Princeton Problems in Physics with Solutions". American Journal of Physics. 60 (5): 477–478. Bibcode:1992AmJPh..60..477N. doi:10.1119/1.16855.
- ↑ "John Edward Ruhl". Astrogen. American Astronomical Society. Retrieved 2023-08-16. See also Ruhl's dissertation at ProQuest 304101104.
- ↑ Rejcek, Peter (April 27, 2015). "A sticky problem: SPIDER seeks clues to the enigma of how the universe first expanded". The Antarctic Sun. United States Antarctic Program. Retrieved 2023-08-16.
- ↑ Hutchison, Kristan (December 1, 2002). "Looking for the dark side of the universe" (PDF). The Antarctic Sun. United States Antarctic Program. Retrieved 2023-08-16.
- ↑ "Scientists Use South Pole Telescope to Produce the Most Detailed Images of the Early Universe". National Science Foundation. December 13, 2002. Retrieved 2023-08-16.
- ↑ Beasley, Dolores (April 29, 2001). "New Boomerang Findings Reveal "Music" of the Early Universe". NASA. Retrieved 2023-08-16.
- ↑ "Fellows nominated in 2005 by the Division of Astrophysics". APS Fellows archive. American Physical Society. Retrieved 2023-08-16.
- ↑ "John Ruhl's commitment to student success earns him Diekhoff Award for Mentoring". The Daily. Case Western Reserve University. May 5, 2016. Retrieved 2023-08-16.
