NASA / ESA / STSCI / R.KENNICUT, U.ARIZONA / SCIENCE PHOTO LIBRARY NASA / ESA / STSCI / R.KENNICUT, U.ARIZONA / SCIENCE PHOTO LIBRARY
Cepheid variable star in M100 galaxy. A new value for the age of the universe of about 8 billion years has been deduced from Hubble Space Telescope observations of this and other 11 Cepheid variable stars in M100. The two images, taken 22 days apart in May 1994, show the change in brightness of a Cepheid star (centre in the frames). The period with which Cepheid stars change their brightness is related to their distance. Astronomers were able to pinpoint the distance of M100 to 56 million light years; this yields a value for the Hubble constant of about 80 km/s per megaparsec & an age of the universe of about 8 billion years.
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