August 11, 1995 The Compton Gamma Ray Observatory Credit: NASA, Compton Gamma Ray Observatory Science Support Center Explanation: The Compton Gamma Ray Observatory (CGRO) was the most massive instrument ever launched by a NASA Space Shuttle and continues to revolutionize gamma-ray astronomy. This orbiting observatory sees the sky in gamma-ray photons - light so blue humans can't see it. These photons are blocked by the Earth's atmosphere from reaching the Earth's surface. Results from CGRO have shown the entire universe to be a violent and rapidly changing place - when viewed in gamma-rays. Astronomers using CGRO data continue to make monumental discoveries, including showing that mysterious flashes of gamma-rays are much more powerful than previously imagined, discovery of a whole new class of QSO, and discovery of objects so strange that astronomers can't yet figure out what they are.