Abstract
Masses, radii and luminosities of distant stars can only be measured accurately in eclipsing binaries. These systems further provide an independent method for calibrating the extragalactic distance scale and thus determining the Hubble constant. They have been used as distance indicators to the Magellanic Clouds, the Andromeda Galaxy and most recently to the Triangulum Galaxy by the DIRECT Project, pushing the limit of our current observational capabilities. Despite their great potential for furthering our understanding of massive stars, the most massive stars in eclipsing binaries remain unexplored. A systematic study of such systems is currently underway. I present results from a photometric survey of the massive Westerlund 1 cluster, a likely host to some of the most massive stars in eclipsing binaries in our Galaxy.
