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Nature22 January 2004

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Pleiades move with the times

The Hipparcos satellite has mapped the positions of over 100,000 stars with much greater accuracy than was previously possible. But there may be a problem. Nearby star clusters such as the Pleiades play an important role in stellar astronomy by providing groups of stars of the same age and distance from the Earth. This is useful when testing theoretical models of star structure and evolution. The distance to the Pleiades became a subject of controversy in 1997, when Hipparcos provided a revised distance measurement 10% smaller than the accepted value. Either something is wrong with the standard models of main sequence stars or, some argued, there is something wrong with some distances being calculated from Hipparcos data. There is a simple classical method available to check the disputed distance to the Pleiades, however. Atlas, one of the brightest stars in the cluster, is a binary, and by determining the orbital parameters with interferometry a precise distance can be calculated. That has now been done, and the results support the 'old' distance to the Pleiades rather than the revised Hipparcos one.

letters to nature
A distance of 133-137 parsecs to the Pleiades star cluster
Nature 427, 326–328 (2004); doi:10.1038/nature02296
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news and views
Astronomy: A problem of distance
How far is the Pleiades star cluster from Earth? The latest measurement suggests that there is a problem with data from the Hipparcos satellite, which will have repercussions for estimating other astronomical distances.
Nature 427, 299–300 (2004); doi:10.1038/427299a
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