During the latter part of last week, a huge void rotated across the face of the sun. But never fear, it isn't a sign of the "End Times" or some weird sci-fi stellar malnourishment, this particular hole is a coronal hole. Though it may be a well-known phenomenon, it is noteworthy - it's the largest coronal hole to be observed in the sun's atmosphere for over a year.
Snapped through three of NASA Solar Dynamics Observatory‘s (SDO) extreme ultraviolet filters, this coronal hole is caused by a low density region of hot plasma.
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The sun's lower corona is threaded with powerful magnetic fields. Some are looped - or "closed" - very low in the corona, creating the beautiful, bright coronal loops that trap superheated gases that generate vast amounts of extreme ultraviolet light, radiation that is produced by multimillion degree plasma (the bright regions in the image, top).
However, there are also "open" field lines that have one end of their magnetic flux anchored in the solar photosphere. These lines fire solar plasma into interplanetary space at an accelerated rate, often intensifying space weather conditions. These regions of open field lines, or coronal holes, act like fire hoses, blasting plasma into space. These regions are the source of the the fast solar wind that accelerates solar material toward Earth, which often only takes 2-3 days to travel from the sun to Earth.
Through the SDO's eyes, coronal holes appear dark as there is a very low density of the multimillion degree plasma generating the EUV radiation. And as this dramatic observation demonstrates, to the eyes of the SDO, the sun really does appear to have a hole.
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We are currently going through an uptick in solar activity as our nearest star experiences "solar maximum" - the peak of its natural 11-year cycle. At this time, we can expect an increased frequency of solar flares and coronal mass ejections as the sun's magnetic field becomes increasingly stressed. Although this solar maximum is less active than predicted, it is producing some powerful flares and CME's. Now we're seeing huge coronal holes, all a consequence of the twisted turmoil our sun is currently enduring.
Image credit: NASA/SDO