... A Mystery in Gamma Rays . ... Credit Copyright: N. Gehrels, D. Macomb, D. Bertsch, D. Thompson, R. Hartman ( GSFC ), EGRET , NASA Explanation: Gamma rays are the most energetic form of light, packing a million or more times the energy of visible light photons. What if you could see gamma rays? ... When the EGRET instrument on the orbiting Compton Gamma-ray Observatory surveyed the sky in the 1990s, it cataloged 271 celestial sources of high-energy gamma-rays. ... Solar Flare in the Gamma ray Sky . ...