Editing Sunspot number (section)

== History ==
Astronomers have been observing the Sun recording information about sunspots since the advent of the telescope in 1609.<ref>{{cite book|first1 = Jose M.|last1 = Vaquero|first2 = M.|last2 = Vazquez|title=The Sun Recorded Through History|publisher=Springer New York|year=2009|isbn=978-0-387-92790-9|doi = 10.1007/978-0-387-92790-9}}</ref>
However, the idea of compiling the information about the sunspot number from various observers originates in [[Rudolf Wolf]] in 1848<ref>{{cite web|title=The Sun - History|url=http://www-istp.gsfc.nasa.gov/Education/whsun.html|date=2001-11-25|access-date=2012-01-08}}</ref> in [[Zürich]], [[Switzerland]]. The produced series initially had his name, but now it is more commonly referred to as the international sunspot number series.

The international sunspot number series is still being produced today at the observatory of Brussels.<ref>[http://sidc.oma.be/ SIDC], RWC Belgium, World Data Center for the Sunspot Index, [[Observatoire Royal de Belgique|Royal Observatory of Belgium]], 'year(s)-of-data'.</ref> The international number series shows an approximate periodicity of 11 years, the [[solar cycle]], which was first found by [[Heinrich Schwabe]] in 1843, thus sometimes it is also referred to as the Schwabe cycle. The periodicity is not constant but varies roughly in the range 9.5 to 11 years.<ref>Using data from [http://sidc.oma.be/index.php3 SIDC] for the last 300 years and running a fast [[Discrete Fourier transform|FFT]] function on the data gives an average maximum at 10.4883 years/cycle.</ref> The international sunspot number series extends back to 1700 with annual values while daily values exist only since 1818.

Since 1 July 2015 a revised and updated international sunspot number series has been made available.<ref>[http://www.stce.be/press/01/welcome.html Switching to the new Sunspot Number (1 July 2015)]</ref>  The biggest difference is an overall increase by a factor of 1.6 to the entire series.  Traditionally, a scaling of 0.6 was applied to all sunspot counts after 1893, to compensate for Alfred Wolfer's better equipment, after taking over from Wolf.  This scaling has been dropped from the revised series, making modern counts closer to their raw values.  Also, counts were reduced slightly after 1947 to compensate for bias introduced by a new counting method adopted that year, in which sunspots are weighted according to their size.<ref name="clette14" />