Solar Activity Revisited (March 25, 2005)
Hi-res TIF image (3.2M)
A check of the sunspot number chart above shows that the number of sunspots continues its slide downwards as we march away from the solar maximum period of peak activity for this 11-year solar cycle. If we compare where we are now with our POTW from February 2004 , we see that the numbers continue to steadily decline along their predicted path. Scientists track solar cycles by counting sunspots - this solar cycle reached its peak level in July 2000. Since then, the number of sunspots and general solar activity have gradually diminished. Inevitably, the number of sunspots will follow this curve down until the numbers bottom out, sometime around 2006 or 2007. Scientists also keep track of solar microwave flux, ultraviolet line emission, flare frequencies, and interplanetary disturbance frequencies as other ways of measuring the solar and heliospheric cycle.
The sunspot chart, developed by David Hathaway and other solar physicists at Marshall Space Flight Center, has been superimposed on a SOHO image of the solar surface taken by its MDI instrument. The upper and lower dotted lines represent the range of prediction and the solid line between them represents the average prediction. The jagged line gives the actual sunspot number as derived by a commonly used formula. Note that the Sun has almost no sunspots on this day, March 22, 2005.
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SOHO began its Weekly Pick some time after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.
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