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Hubble constant

   Also found in: Encyclopedia, Wikipedia, Hutchinson 0.01 sec.
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Noun1.Hubble constant - (cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer; the Hubble constant is not actually a constant, but is regarded as measuring the expansion rate today
cosmogeny, cosmogony, cosmology - the branch of astrophysics that studies the origin and evolution and structure of the universe
constant - a number representing a quantity assumed to have a fixed value in a specified mathematical context; "the velocity of light is a constant"

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Since measurements of the distances to galaxies are uncertain, however, the Hubble constant isn't known to an accuracy better than 10 percent, and the age of the universe derived using this method is plagued by the same uncertainty.
The rate of expansion of the universe is described by the Hubble constant (the ratio of the speed at which a galaxy is receding from the earth to its distance from the earth); its measurement and actual value have long been a topic of cosmological controversy, with professional bragging rights, as well as the age and ultimate fate of the universe, on the line.
While he welcomes time-delay measurements that are more accurate, he says astronomers must better determine how mass is distributed in each lens before they can convert the data into a new estimate of the Hubble constant.
 
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