NASA’s Solar Dynamics Observatory (SDO) came across an oddity that the spacecraft has rarely observed before: a dark filament encircling an active region (October 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.
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