The Distance to the Large Magellanic Cloud

Science 18 August 2000: Vol. 289 no. 5482 pp. 1149-1150 DOI: 10.1126/science.289.5482.1149 Perspective ASTRONOMY The Distance to the Large Magellanic Cloud Andrew A. Cole* - Author Affiliations The author is in the Department of Astronomy, University of Massachusetts, 532A LGRT, Amherst, MA 01003, USA. E-mail: cole@condor.astro.umass.edu 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 (dlmc) remains uncertain to within roughly ±10%. This uncertainty in dlmc 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 dlmc 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 dlmc = 50 kiloparsecs (1 kpc = 3260 light years = 3.09 × 1016 km) was adopted in the project, but the relevance of this value remains a matter of dispute