Another Step
Cepheus, the king, climbs high across the northern sky on August evenings, just along the edge of the Milky Way. It's not that much to look at, but one of its stars is crucial to the effort to determine the scale of the universe. And astronomers recently measured the star's distance with unprecedented accuracy.
The star is Delta Cephei. It's the prototype of a class of stars that pulse like beating hearts.
As a Cepheid star pulses, it gets brighter and fainter. And there's a direct relationship between the length of a "beat" and a Cepheid's true brightness - and that's the key to using them as distance markers. If you can use other techniques to get accurate distances to a few of these stars, then you can determine how truly bright they get. And with that information, you can measure how bright the Cepheids in other galaxies appear, then calculate how far away they are.
But it's been hard to measure the distances to the Cepheids in our own galaxy. Various estimates to Delta Cephei, for example, have varied by hundreds of light-years.
A team led by Texas astronomer Fritz Benedict recently measured the distance with Hubble Space Telescope. The team found that Delta Cephei is 890 light-years away, give or take about 30 light-years.
This summer, the astronomers finished measuring the distances to 10 other Cepheids. Their results should be ready to publish by year's end - results that will help to take the measure of the universe.
Script by Damond Benningfield, Copyright 2005
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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