A coronal hole is a region on the sun's atmosphere (the corona) that has a lower density and temperature compared to the surrounding areas. These holes appear dark in images taken in ultraviolet (UV) and X-ray wavelengths. Coronal holes are associated with open magnetic field lines, allowing solar wind—streams of charged particles (mostly electrons and protons)—to escape into space at high speeds. Coronal holes can vary in size and can last for days to months.
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