RHESSI/X-ray Imaging Spectrometer
The RHESSI instrument is an imaging spectrometer observing the Sun at X-ray to gamma-rays (photon energies of 3 keV to 17 MeV) at time resolutions of a few seconds. (eV
stands for "electron volt" and is a unit of energy. Note that photons of visible light have energies of 2-3 eV. 1 keV is a thousand electron volts and 1 MeV is a million electron volts.