A sequence of images captured by NASA's Solar Dynamics Observatory spacecraft shows the Sun in different wavelengths. Three of the images show a prominent coronal hole toward the top of the Sun, where solar particles have blown outward into space leaving a dark, relatively cool region. A fourth image adds a map of magnetic field lines. (Source: NASA) Every once in awhile, a kind of hole blows out in the Sun's atmosphere — a "coronal hole," as it is called. And it has happened again, this time on top of the Sun. You can see it above in a sequence of images captured by NASA's Solar Dynamics Observatory spacecraft, or SDO, in different wavelengths of light. Look for the big dark area on the Sun's cap. Not to worry! This is completely normal.
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Ordinarily, the Sun's magnetic field lines extend up through ...
