Like cosmic lighthouses shining through fog on an astral beach, a clump of quasars lit the way to a supercluster of galaxies that could be the biggest structure of the early universe, astronomers said on Monday. If the cluster were visible with the naked eye from Earth, it would cover a region about two by five degrees in size in the night sky, or about 40 times the area of the full moon, scientists from NASA's Goddard Space Flight Center and the National Optical Astronomy Observatories in Arizona reported.