b'Distance to the Large Magellanic Cloud Refined to One Percent18Both the Large and Small Magellanic Clouds can be seen at left in this view of the twin Magellan telescopes at Carnegies Las Campanas Observatory in Chile. Image courtesy Yuri Beletsky, Carnegie Institution for ScienceA stronomers study the scale and expansionaccurate measurement of the distance to the LMC rate of the universe by observing nearbyallows a more precise calibration of the Leavitt Law, standard candles, objects with a knownwhich is used extensively in measuring distances to luminosity, or brightness. These standard candlesmore distant galaxies. Ian Thompson and team have are then used to determine the distances to objectsbeen studying 20 eclipsing binary stars in the LMC, much farther away.and they have doubled the precision of measuring the distance to this galaxyfrom 2% to 1%. The Large Magellanic Cloud (LMC), a nearby galaxy, hosts a rich population of standard candles,To determine their accurate distance to the LMC, particularly Cepheid variable stars. It is importantThompson and team measured an improved to the calibration of extragalactic distances and incalibration of the relationship between the surface determining the expansion rate of the universe, calledbrightness and color of helium-burning giant stars. the Hubble Constant. The current uncertainty in theThey then carefully selected 20 eclipsing binary Hubble Constant is dominated by the uncertainty ofstars in the LMC from a catalog of 35 million stars. the calibration of the relationship between the periodEach component of the binaries is similar to their and luminosity of Cepheids (the Leavitt Law). Ancalibrating stars.'