Black holes do not emit any light, for their gravity does not allow any to escape. They do, however, emit gamma rays, which we can detect and use to discover great volumes of information about them. Quasars, pulsars, neutron stars and distant galaxies can also be studied using gamma rays. Light and other types of waves will become very weak after traveling great distances. Gamma rays, however, contain much more energy, and their signals will remain stronger for longer distances.
Atmospheric interference prevents ground-based gamma ray telescopes from being used effectively.
Therefore, most gamma ray observation is done from satellites outside of our atmosphere. The main tool used to detect gamma rays is the Compton Gamma Ray Observatory. Since its launching five years ago, it has uncovered large amounts of information about the universe. Interactions of gamma rays from space with the lunar surface were observed. According to this apparatus and high-energy gamma rays, the moon is much brighter than the sun.