Over-achieving sunspot group 656 (August 19, 2004)
Hi-res TIF image (2.4M).
Over a period of just five days, August 8-14, 2004, Active Region 656 went from a middling-sized group to a powerhouse with the area of nearly 20 Earths. The split screen Sun stills show how dramatically the group changed. Sunspots are areas of intense magnetic activity that can last from days to months and are always changing. Notice in the movie (over the longer period Aug. 8-16) that the Sun's rotation has moved the group from near the left side of the Sun most of the way around to the right side. This regular movement of sunspots was the first indication to observers on Earth that the Sun in fact rotated. Careful measurements showed that the rotation period of sunspots is about 27 days, though the visible surface of the Sun actually rotates a bit faster at the Sun's equator, and considerably slower near the solar poles.
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