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.

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PIA22104_Encircling_Filament_big.mp4
PIA22104_Encircling_Filament_sm.mp4

SDO is managed by NASA's Goddard Space Flight Center, Greenbelt, Maryland, for NASA's Science Mission Directorate, Washington. Its Atmosphere Imaging Assembly was built by the Lockheed Martin Solar Astrophysics Laboratory (LMSAL), Palo Alto, California.