The number of sunspots increases and decreases over time in a regular, approximately 11-year cycle, called the sunspot cycle. The exact length of the cycle can vary. It has been as short as eight years and as long as fourteen, but the number of sunspots always increases over time, and then returns to low again. This video is public domain and can be downloaded at: http://svsdev.gsfc.nasa.gov/goto?10804 Like our videos? Subscribe to NASA's Goddard Shorts HD podcast: http://svs.gsfc.nasa.gov/vis/iTunes/f0004_index.html Or find NASA Goddard Space Flight Center on Facebook: http://www.facebook.com/NASA.GSFC Or find us on Twitter: http://twitter.com/NASAGoddard
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