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Basic Astronomy Concepts


Redshift, distant galaxies, astronomers, galaxy, Dust particles

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>  What Is Redshift

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Redshift, change, or shift, in the light radiated by an object, such as a star or galaxy, that indicates the objectís motion. Scientists have used redshifts to measure the velocities (speed and direction) of distant galaxies. Knowing the velocities of galaxies helps astronomers understand how the universe is changing. This knowledge allows scientists to interpret the distant past of the universe and to predict the universeís distant future.

Redshift only occurs when an object is moving. Another mechanism can also redden the light of astronomical objects, but it is not considered to be the same as redshift. Dust particles between stars are just the right size to scatter light with short wavelengths more than they scatter light with long wavelengths. As the light of a star passes through a cloud of dust on the lightís way to Earth, more of the long, red wavelengths get through the dust than the short, blue wavelengths do. This makes the star appear redder than it really is, but the light that reaches Earth is the true red light of the star and has not actually shifted.


Silk, Joseph I., B.A., M.A., Ph.D.

Professor, Physics and Astronomy, University of California at Berkley. Author of "The Left Hand of Creation" and other books.

Article key phrases:

Redshift, distant galaxies, astronomers, galaxy, Dust particles, universe, motion, distant past, distant future, right size, mechanism, Earth, direction, Scientists, object, speed, stars, knowledge, way, light, change

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