Associated Press Tuesday, January 9, 2001 SAN DIEGO -- Astronomers have found what may be the largest structure in the observable universe an immense concentration of quasars and galaxies clustered across more than 600 million light years. [...] "We have found nothing bigger in the [astronomy] literature, and nobody has brought to our attention anything bigger," said Gerard Williger, a National Optical Astronomy Observatories researcher now working at NASA's Goddard Space Flight Center in Greenbelt, Md. He presented his study Monday at the national meeting of the American Astronomical Society. When viewed from Earth, the cluster is just below the center of the constellation Leo the Lion. It spans an area of the sky of two degrees by five degrees, an area about 40 times that of the full moon as seen from Earth. [...]