Rare Encircling Filament

NASA's Solar Dynamics Observatory came across an oddity this week that the spacecraft has rarely observed before: a dark filament encircling an active region (Oct. 29-31, 2017). Solar filaments are clouds of charged particles that float above the sun, tethered to it by magnetic forces. They are usually elongated and uneven strands. Only a handful of times before have we seen one shaped like a circle. (The black area to the left of the brighter active region is a coronal hole, a magnetically open region of the sun). While it may no major scientific value, it is noteworthy because of its rarity. The still and video clip were taken in a wavelength of extreme ultraviolet light. Movies are available at https://photojournal.jpl.nasa.gov/catalog/PIA22104