Editing Sunspot (section)

=== Solar cycle ===
{{main|Solar cycle}}
[[Image:Sunspot butterfly graph.gif|thumb|upright=1.35|[[Solar cycle#Sunspots|Butterfly diagram]] showing paired [[Spörer's law]] behavior|alt=Point chart showing sunspot area as percent of the total area at various latitudes, above grouped bar chart showing average daily sunspot area as % of visible hemisphere.]]
[[File:Sunspot Growth in June 2012.ogv|left|thumb|The full solar disk over the course of 13 days during the rise of [[solar cycle 24]]]]

Solar cycles last typically about eleven years, varying from just under 10 to just over 12 years. Over the solar cycle, sunspot populations increase quickly and then decrease more slowly. The point of highest sunspot activity during a cycle is known as solar maximum, and the point of lowest activity as solar minimum. This period is also observed in most other [[Solar phenomena|solar activity]] and is linked to a variation in the solar magnetic field that changes polarity with this period.

Early in the cycle, sunspots appear at higher latitudes and then move towards the equator as the cycle approaches maximum, following [[Spörer's law]]. Spots from two sequential cycles co-exist for several years during the years near solar minimum. Spots from sequential cycles can be distinguished by direction of their magnetic field and their latitude.

[[Wolf number|The Wolf number]] sunspot index counts the average number of sunspots and groups of sunspots during specific intervals. The 11-year solar cycles are numbered sequentially, starting with the observations made in the 1750s.<ref name="testtest1">{{cite book
| author=Tribble, A.  |date=2003
| title=The Space Environment, Implications for Spacecraft Design
| publisher=Princeton University Press | pages=15–18}}</ref>

[[George Ellery Hale]] first linked magnetic fields and sunspots in 1908.<ref name="doi10.1086/141602">{{Cite journal | last1 = Hale | first1 = G. E. | title = On the Probable Existence of a Magnetic Field in Sun-Spots | journal = The Astrophysical Journal | volume = 28 | pages = 315 | year = 1908 | doi = 10.1086/141602|bibcode = 1908ApJ....28..315H | doi-access = free }}</ref> Hale suggested that the sunspot cycle period is 22&nbsp;years, covering two periods of increased and decreased sunspot numbers, accompanied by polar reversals of the solar magnetic [[dipole]] field. [[Horace W. Babcock]] later proposed a qualitative model for the dynamics of the solar outer layers. The [[Babcock Model]] explains that magnetic fields cause the behavior described by Spörer's law, as well as other effects, which are twisted by the Sun's rotation.