Active Sun, composite image. This image combines observations from several telescopes. High-energy X-rays from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) are shown in blue; low-energy X-rays from Japan's Hinode spacecraft (X-ray Telescope) are green; and extreme ultraviolet light from NASA's Solar Dynamics Observatory (SDO, Atmospheric Imaging Assembly) is yellow and red. These observations were made on 29 April 2015. During the observations, microflares occurred; smaller versions of solar flares NuSTAR is being used to study microflares, as well as hypothesized nanoflares, which are even smaller.