Baffled by Astronomy
Astronomers have discovered an enormous concentration of quasars and galaxies clustered across more than 600 million light years. It may be the largest structure in the observable universe, said Gerard Williger, a National Optical Astronomy Observatories researcher now working at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
My question is - if these things are 600 million light years away/across, and signals take that time to get to Earth – how do they know it’s still there?