Monday, November 19, 2012

The Minimalists

The German Gustav Spörer (1822-1885), who had studied mathematics and astronomy, began as a school teacher but then, at age 36, turned to astronomical observation. His interest centered on the sun and using sunspots to discover where the sun’s equator lies. His work led him to discover, searching ever older records, that a period from 1645 to 1715 the sun had virtually no sunspots. Nobody paid much attention. The younger Edward Maunder (1851-1928), an English astronomer, later made the same observations and was a much better publicist—perhaps because his second wife, Annie Russell, helped him. As a consequence, that period of minimum sunspots came to be known as the Maunder Minimum. Spörer, however, managed to get his own minimum—posthumously. John A. Eddy (1931-2009), discovered a yet earlier period of solar inactivity dating from 1460 to 1550, and, having a kindly temperament, presumably, he named it after Spörer to make up for that pioneer’s lack of recognition.

Having mentioned these names, we’re far from exhausting discoveries of solar minima, thus periods of unusually low sunspot activity. We also have the Oort Minimum, dated to 1010-1050 and associated with the Dutch astronomer Jan Oort (1900-1992), the Wolf Minimum, dated to 1280-1350, associated with Swiss astronomer Rudolf Wolf (1816-1893), and the Dalton Minimum, 1790-1820, named after the English chemist, physicist and meteorologist John Dalton, but I cannot discover who actually made the observations and named this minimum after him. The period from 1300 to 1850, thus encompassing the Spörer-Maunder minima and what might be called the Dalton Dip are known as the Little Ice Age.

I show above a graphic from Wikipedia (link) charting carbon-14 measurements from about 850 AD to 1950. These are thought to be meaningful because sunspot activity interferes with cosmic-rays. Therefore fewer rays reach the earth in periods of strong sunspot activity—and therefore produce less carbon-14. The more quiet the sun, the more radiocarbon is formed. This gives us a way of measuring, indirectly, sunspot activity down here on earth. The graphic above does not single out the Dalton Minimum, but it is there to the right of the 1800 peak.

Now we have ample, indeed abundant, evidence that solar maxima are warm periods while solar minima, if they last a while, produce a cooler climate; hence we look back on a Little Ice Age. Currently, what with a very wide trough in the last solar cycle, the 23th, and a “weak” 24th underway now, some NASA-ites have speculated that we may be seeing another Dalton. Interesting. We’ll have to wait. It might be ironical that just as the population finally gets with Global Warming, the New York Harbor might freeze over as it did in 1780. (See also my post today on LaMarotte.)

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