Astronomy & the X-ray and gamma ray spectrum. This part of the electromagnetic spectrum contains gamma rays (left) & X-rays (right). X-rays border on extreme ultraviolet (far right). They are absorbed by atoms in the atmosphere. Gamma rays can penetrate far enough to be detected by high- altitude balloons. High-energy (short wavelength) gamma rays create pulses of light (Cerenkov radiation, bottom left) that can be detected from the ground. X-rays & gamma rays can also be detected by instruments in spacecraft above the atmosphere. Sources of X-rays & gamma rays include the Sun (centre right), galactic clusters (upper centre) and supernova remnants (far right).