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PERSPECTIVES: ASTRONOMY
After nearly a century of argument, astronomers may soon be able to agree on the distance to the most important cosmic milepost, the Large Magellanic Cloud (LMC). This larger of two nearby galaxies is gravitationally bound to the Milky Way and visible to observers in the Southern Hemisphere.
The LMC gained-its cosmological importance because it is a convenient benchmark for extragalactic distances; nearly all extragalactic distances measured to date are only known relative to the distance from Earth to the LMC. Despite its importance in observational cosmology, however, the distance to the LMC (dim) remains uncertain to within roughly 10%. This uncertainty in dInI, propagates directly into an uncertainty in the expansion rate of the universe, which in turn confounds attempts to reconstruct the history and predict the fate of the universe. The confusion over dim is the single largest source of error for the recently completed Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale, whose goal was to determine the Hubble constant to within 10%. A mean value of d^sub lmc^ = 50 kiloparsecs (I kpc = 3260 light years = 3.09 x 10^sup 16^ km) was adopted in the project, but the relevance of this value remains a matter of dispute (1).
Toward an accurate estimate of cosmological distance. The radial velocity and light curves of an eclipsing binary star system allow the determination of their relative masses and radii; spectroscopy allows determination of their temperatures. The absolute distance from Earth then follows from a simple formula.
The true value of dl,, has remained enigmatic because measurements show no tendency to cluster about a well-defined mean value but rather show a broad...