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In astronomy, the Tully-Fisher relation, published by astronomers R. Brent Tully and J. Richard Fisher in 1977, is a standard candle that measures the distance to rotating spiral galaxies by the width of the galaxy's spectral lines. The empirically-derived relation that the luminosity of a galaxy is directly proportional to the fourth power of its rotational velocity, which can be calculated from the width of the spectral line, and uses the distance modulus to find distance from luminosity and apparent magnitude.The reasoning behind the relation first states that the wider a spectral line for a galaxies, especially the 21- cm hydrogen line, the faster the galaxy is rotating. This is because the side spinning toward us will have a slight blueshift and the side spinning away from us will have a slight redshift as compared to the average spectral line position for the galaxy as a whole. Furthermore, since the galaxy's centrifugal force, which depends on rotational velocity, and gravitation, which depends on mass, are in balance, the mass and rotational velocity are related. Then, the relation assumes that more massive galaxies tend to have proportionally greater absolute luminosities, from which and the apparent magnitude the distance to a galaxy can be calculated.
1 See also
- distance modulus
- standard candle
- Modified Newtonian dynamicsThe modified Newtonian dynamics (MOND is a physical theory which attempts to explain the galaxy rotation problem by changing Newton's law of motion. The more mainstream approach to explain this problem postulates the existence of dark matter. MOND was pro
2 References
- zebu.uoregon.edu/~imamura/209/apr7/TF.html
- Kuhn, Karl F., In Quest of the Universe. BooksEnthsiast.com.
- 2003 C-level Astronomy Presentation for Science OlympiadThis article is about the Science Olympiad competition for secondary schools in the United States. For information on the science olympiads such as the International Physics Olympiad or the International Chemistry Olympiad, see International science olymp ( Microsoft PowerPointMicrosoft PowerPoint is a popular presentation program developed for the Microsoft Windows and Mac OS computer operating systems. Being widely used by businesspeople, educators, and trainers, it is among the most prevalent forms of persuasion technology: format, openable in OpenOffice.orgOpenOffice. org OOo (the ". org" inclusion is due to a trademark dispute) is an office applications suite. It is intended to be compatible, and directly compete, with Microsoft Office. OOo is free software under the LGPL or SISSL and is available for Micr)
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