Hubble Constant - Research Article from Macmillan Science Library: Space Sciences

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Cepheid Variables

The most precise method for measuring distances is based on the observations of Cepheid variables, stars whose atmospheres pulsate regularly for periods ranging from 2 to about 100 days. Experimentally it has been established that the period of pulsation is correlated with the brightness of the star. High resolution is the key to discovering Cepheids in other galaxies—in other words, the telescope must have enough resolving power to distinguish Cepheids from other stars that contribute to the overall light of the galaxy. The resolution of the Hubble Space Telescope is about ten times better than can be generally obtained through Earth's turbulent atmosphere.

The reach of Cepheid variables as distance indicators is limited, however, even with the HST. For distances beyond 20 megaparsecs or so, brighter objects than ordinary stars are required; for example, bright supernovae or the brightnesses of entire galaxies. The absolute calibration for all...

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This section contains 575 words
(approx. 2 pages at 300 words per page)
Buy the Hubble Constant Encyclopedia Article
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Macmillan Science Library: Space Sciences
Hubble Constant from Macmillan Science Library: Space Sciences. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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