With nearly eighteen centuries of naked eye observations of sunspot activities, scientists have a treasure trove of information about solar activity. The first person to realize that collating multiple sources of historical information about solar sunspot activity could yield results was astronomer Rudolf Wolf who published the “Wolf Sunspot Numbers” that contained information from 1715-1893. With the advances in knowledge about sunspots including their causation by magnetic flux and their association with the issue of global warming, it is not surprising to find much interest and heated debate over the subject. Recent findings note that sunspot activity varies in amplitude, lengths of cycles, magnetic polarity of sunspots and the solar equatorial rotation rates.
Sunspot Minimums
Sunspot minimums are places in the historical record where no sunspot activity occurs. Edward (Walter) Maunder, an astronomer at the Royal Greenwich Observatory verified that there was no sunspot activity recorded between AD 1645 and 1715 which is known as the Maunder Minimum. The Sporer Minimum, named for astronomer Gustav Friedrich Wilhem, Sporer, is a period between AD 1420 and 1570 with low sunspot activity based on Carbon-14 records in tree rings and auroral activity. The Dalton Minimum, named for meteorologist John Dalton, is a period between 1790 to 1830 with low solar activity that corresponded to lower-than-average global temperatures.
Sunspot Maximum
Concluding in 2005, a cycle of increasing sunspot activity ended. This current cycle is the one most noted for the public controversy over global warming. The main issue behind global warming is the main extent to which man has contributed to the warming of the planet.
Sunspot Cycles
Sunspot activity appears to by cyclical with various useful information supporting or being derived from those cycles. The Scwabe Cycle and the Hale cycle are widely accepted. The Gleissberg Cycle and 200-year cycle are being debated, i.e. more information is needed to determine the usefulness of these cycles.
Schwabe Cycle
Pharmacist Heinrich Schwabe’s amateur astronomy study discovered that sunspots follow an approximately 11 year cycle. This cycle varies from 9 to 14 years at times and led to Rudolf Wolf’s work on sunspot cycles.
Hale Cycle
Astronomer George Ellery Hale discovered a 22-year cycle exists in which the magnetic polarity of sunspot pairs reverse from North to South and then returns (first positive leading than negative leading) halfway through the cycle.
The Gleissberg cycle
A 79.2 year cycle in which the latitudinal component of sunspot activities varies.[4]
200-year Cycle
An 200 year cycle associated with the gravitational affects of Jupiter that encompasses the Hale cycle and the Schwabe cycle.[5]
Studies on solar sunspot activities aren’t complete and clearly have much more information to provide scientists.
[1] David Darling, The Universal Book of Astronomy
[2] Birney, Gonzalez, Oesper, Observational Astronomy
[3] Wikipedia
[4] Javariah, Bertello, Ulrich, “Long-term variations in solar differential rotation and sunspot activity
[5] Timo Niroma, Sunspots
