The sun produces energy by fusing hydrogen in its core, so the layers surrounding the core generally get cooler as you move outwards—with one exception.
July 08 | 2017
This filament on the sun, a giant ribbon of relatively cool solar material, threads through the corona, the sun's atmosphere. The individual threads that make up the filament are clearly discernible in this photo. This image, captured by the Solar Optical Telescope onboard JAXA/NASA’s Hinode solar observatory, has made a significant step towards understanding why the corona—the outermost, wispy layer of the sun's atmosphere—is hundreds of times hotter than the lower photosphere. Image Credit: JAXA/NASA/Hinode