The image above shows an oddity that NASA’s Solar Dynamics Observatory has rarely observed before: a dark filament encircling an active region, spotted in late October this year.
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 scientists 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.