海角大神

Space photos of the day 08/30

08/30/2010 10:33 am ET This ominous, dark shape sprawling across the face of the Sun is a coronal hole - a low density region extending above the surface where the solar magnetic field opens freely into interplanetary space. Studied extensively from space since the 1960s in ultraviolet and x-ray light, coronal holes are known to be the source of the high-speed solar wind, atoms and electrons which flow outward along the open magnetic field lines. During periods of low activity, coronal holes typically cover regions just above the Sun's poles.