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Last Post 3/18/2008 1:56 PM by  Emilia Kilpua
sunspots & cycle
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3/17/2008 8:45 AM

    Margie (LM)

    Why are sunspots measured in terms of numbers, that is how many at any given time, and how it corresponds to the solar cycle?

    thank you


    Dawn Myers



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    Posts:151
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    3/17/2008 11:02 AM
    Hello Margie Sunspots are given a number by the Space Environment Center, a part of NOAA. They are numbered sequentially as they are identified. If a group rotates around the far side of the Sun and then rotates back into view it is given a new number when it is spotted again. Pat McIntosh was the solar physicist who started the number system back in the mid 1960s.

    Emilia Kilpua



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    3/18/2008 1:56 PM
    Hi Margie! The number of sunspots describes the level of the solar activity. When there are many sunspots the overall Sun’s activity is at the maximum, for example several flares and coronal mass ejection occur every day at that time. When there are only few sunspots (like now!) the solar activity is very weak. Solar activity as well as the sunspot number varies in about 11-year cycle. Sun’s equator rotates faster than the poles and this is the main cause of systematic variations in the solar activity. The complex rotation wounds up the magnetic fields and when the tubes of strong,twisted magnetic fields rise up to the Sun’s surface they appear as sunspots. At solar maximum the Sun's magnetic field is very complex and active regions around the sunspots often erupt to flares and coronal mass ejections.
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