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Re: Measuring Space

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Posted by RFL on August 20, 1998 13:38:36 UTC

"Normal" stars obey a mass - luminosity law that has been very well established for stars on the main sequence in the H-R diagram. Similarly, the oscillations of a Cepheid closely follow a mass - period relationship as well. This relationship is of major significance in measuring distances. Once the period of a Cepheid is known, we can deduce its absolute magnitude M; but the apparent magnitude m is linked to M and the distance d by:

m - M = 5(logd - 1)

The magnitude m is given by observation; once M is known, the distance of the Cepheid may be deduced. Cepheids are giants, which are visible at great distances. Once a Cepheid is detected in a cluster or in a nearby galaxy, the distance of the object is immediately known.

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