This chart depicts the electromagnetic spectrum, highlighting the X-ray portion. NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's XMM-Newton telescope complement each other by seeing different colors of X-ray light. XMM-Newton sees X-rays with energies between 0.1 and 10 kiloelectron volts (keV), the "red" part of the spectrum, while NuSTAR sees the highest-energy, or "bluest," X-ray light, with energies between 3 and 70 keV. Doctors and dentists generally use X-rays in this higher energy range because they penetrate skin and can only be stopped by dense bones.
NASA's Chandra X-ray Observatory sees a similar energy range as XMM-Newton, but it is better suited for imaging. XMM-Newton specializes in capturing spectral information.