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Old 12-06-2012, 06:23 PM   #228 (permalink)
NeilBlanchard
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The magnetic poles of the sun are stable for 11 years and then they switch, and go another 11 years, and then switch back to the way the cycle started. A cycle is the length of time to go from one state to a different state - and then back to the first state. The full solar cycle is 22 years - and this is the cycle of solar output. It is the length of time that is embedded in sedimentary rock on earth - they are like tree rings and they show a 22 year long cycle.

Quote:
The modern understanding of sunspots starts with George Ellery Hale, who first linked magnetic fields and sunspots in 1908.[14] Hale suggested that the sunspot cycle period is 22 years, covering two polar reversals of the solar magnetic dipole field.
http://en.wikipedia.org/wiki/Sunspot#Physics

Edit: here's another related NOVA program:

http://www.pbs.org/wgbh/nova/earth/extreme-ice.html
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Last edited by NeilBlanchard; 12-06-2012 at 09:24 PM.. Reason: typo