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[[Image:Zurich sunspot number since 1750.png|thumb|350px|Wolf number since 1750.]] | |||
The '''Wolf number''' (also known as the '''International sunspot number''', '''relative sunspot number''', or '''Zürich number''') is a quantity that measures the number of [[sunspots]] and groups of sunspots present on the surface of the sun. | |||
The idea of computing sunspot numbers was originated by [[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|accessdate=2012-01-08}}</ref> in [[Zurich]], [[Switzerland]] and, thus, the procedure he initiated bears his name (or place). The combination of sunspots and their grouping is used because it compensates for variations in observing small sunspots. | |||
This number has been collected and tabulated by researchers for over 150 years. They have found that sunspot activity is cyclical and reaches its maximum around every 9.5 to 11 years (note: Using data from [http://sidc.oma.be/ SIDC] for the last 300 years and running a [[Discrete Fourier transform|FFT]] function on the data gives an average maximum at 10.4883 years/cycle).<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> This cycle was first noted by [[Heinrich Schwabe]] in 1843. | |||
The relative sunspot number <math>R</math> is computed using the formula (collected as a daily index of sunspot activity): | |||
: <math>R = k(10g + s) \, </math> | |||
where | |||
* <math>s</math> is the number of individual spots, | |||
* <math>g</math> is the number of sunspot groups, and | |||
* <math>k</math> is a factor that varies with location and instrumentation (also known as the ''observatory factor'' or the ''personal reduction coefficient'' <math>K</math>).<ref>[http://www.sidc.be/news/106/sunspotnumberclarified.pdf personal reduction coefficient K]</ref> | |||
==See also== | |||
* [[Solar variation]] | |||
* [[Joy's Law (astronomy)]] | |||
==References== | |||
{{reflist}} | |||
==External links== | |||
* [http://cse.ssl.berkeley.edu/segwayed/lessons/sunspots/ The Exploratorium's Guide to Sunspots] | |||
* [http://sidc.oma.be/index.php3 RWC Belgium World Data Center for the Sunspot Index] | |||
* [http://solarscience.msfc.nasa.gov/SunspotCycle.shtml NASA Solar Physics Sunspot Cycle page] and [http://solarscience.msfc.nasa.gov/greenwch/spot_num.txt Table of Sunspot Numbers (txt)] by month since 1749 CE | |||
{{The Sun}} | |||
[[Category:Stellar phenomena]] | |||
[[Category:Solar phenomena]] | |||
[[de:Sonnenfleck#Sonnenflecken-Relativzahl]] | |||
Revision as of 01:00, 22 January 2014
The Wolf number (also known as the International sunspot number, relative sunspot number, or Zürich number) is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the sun.
The idea of computing sunspot numbers was originated by Rudolf Wolf in 1848[1] in Zurich, Switzerland and, thus, the procedure he initiated bears his name (or place). The combination of sunspots and their grouping is used because it compensates for variations in observing small sunspots.
This number has been collected and tabulated by researchers for over 150 years. They have found that sunspot activity is cyclical and reaches its maximum around every 9.5 to 11 years (note: Using data from SIDC for the last 300 years and running a FFT function on the data gives an average maximum at 10.4883 years/cycle).[2] This cycle was first noted by Heinrich Schwabe in 1843.
The relative sunspot number is computed using the formula (collected as a daily index of sunspot activity):
where
- is the number of individual spots,
- is the number of sunspot groups, and
- is a factor that varies with location and instrumentation (also known as the observatory factor or the personal reduction coefficient ).[3]
See also
References
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External links
- The Exploratorium's Guide to Sunspots
- RWC Belgium World Data Center for the Sunspot Index
- NASA Solar Physics Sunspot Cycle page and Table of Sunspot Numbers (txt) by month since 1749 CE
de:Sonnenfleck#Sonnenflecken-Relativzahl
- ↑ Template:Cite web
- ↑ SIDC, RWC Belgium, World Data Center for the Sunspot Index, Royal Observatory of Belgium, 'year(s)-of-data'.
- ↑ personal reduction coefficient K