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Summary
This figure summarizes
sunspot number observations. Since c. 1749,
continuous monthly averagesdead link of
sunspot activity have been available and are shown here as reported by the Solar Influences Data Analysis Center,
World Data Center for the Sunspot Index, at the
Royal Observatory of Belgium. These figures are based on an average of measurements from many different observatories around the world. Prior to 1749, sporadic observations of sunspots are available. These were compiled and placed on
consistent monthly framework by Hoyt & Schatten (1998a, 1998b).
The most prominent feature of this graph is the c. 11 year
solar magnetic cycle which is associated with the natural waxing and waning of solar activity.
On longer time scales, the
sun has shown considerable
variability, including the long
Maunder Minimum when almost no sunspots were observed, the less severe
Dalton Minimum, and increased sunspot activity during the last fifty years, known as the
Modern Maximum. The causes for these variations are not well understood, but because sunspots and associated
faculae affect the brightness of the sun, solar
luminosity is lower during periods of low sunspot activity. It is widely believed that the low solar activity during the Maunder Minimum may be among the principal causes of the chilly
Little Ice Age, circa 1350-1850 A.D.
Copyright
This figure was prepared by
Robert A. Rohde and is part of the Global Warming Art project.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the
Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.http://www.gnu.org/copyleft/fdl.htmlGFDLGNU Free Documentation Licensetruetrue
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This licensing tag was added to this file as part of the GFDL
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References
Hoyt, D. V., and K. H. Schatten (1998a). "Group sunspot numbers: A new solar activity reconstruction. Part 1.". Solar Physics179: 189-219.
Hoyt, D. V., and K. H. Schatten (1998b). "Group sunspot numbers: A new solar activity reconstruction. Part 2.". Solar Physics181: 491-512.
I added another decade to the graph (through Oct., 2015). I started with the previous version was uploaded in 2006. Because it was almost a decade old, it lacked Solar Cycle 24. So I started with that version, and pasted a properly-scaled version of h...
I added another decade to the graph (through Oct., 2015). I started with the previous version was uploaded in 2006. Because it was almost a decade old, it lacked Solar Cycle 24. So I started with that version, and pasted a properly-scaled version of h...