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Hubble constant

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Hubble constant

In astronomy, measure of the rate at which the universe is expanding, named after US astronomer Edwin Hubble. Observations suggest that galaxies are moving apart at a rate of 50–100 kps/30–60 mps for every million parsecs (megaparsecs) of distance. This means that the universe, which began at one point according to the Big Bang theory, is between 10 billion and 20 billion years old. Observations by the Hubble Space Telescope in 1996 produced a figure for the constant of 73 kps/45 mps per megaparsec. Measurements of the cosmic background radiation currently give a value close to 70 kps/43.5 mps per megaparsec.



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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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