New yardstick applied to distant stars

17 Jun 2002

The Hipparcos Star Catalog offers new measurements of the distances to thousands of stars. Of special interest are the distances to Cepheid variable stars, whoseluminosity behavior is used as a yardstick for deducing the distances to far-away galaxies. Launched in 1989, the Hipparcos satellite records theposition on the sky ofmore than 100,000 stars with milli-arcsecond accuracy (a 100-fold improvement over present catalogs) and lesser positional accuracy for a million more stars.

This greater knowledge of star locations is quickly being put to use. For example, stellar ageand distance revisions based on the Hipparcos results, recentlyannounced at a meeting of the Royal Astronomical Society in London, suggest that the globular cluster stars, thought to bethe oldest stars in our galaxy, may be only11 (not 15) billion years old and, furthermore, that the universe as a whole is perhaps 10% older than earlier studies implied. Thus the embarrassing dilemma inwhich globular cluster stars appeared to be older than the universe itself may now be resolving itself.