NASA's Solar Dynamics Observatory came across an oddity 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 have no major scientific value, it is noteworthy because of its rarity. The still was taken in a wavelength of extreme ultraviolet light.
Explore further: Image: NASA's Solar Dynamics Observatory watches a sunspot