The Little Ice Age: How Climate Made History 1300-1850 by Brian Fagan

Author:Brian Fagan
Language: eng
Format: epub
Published: 2011-11-30T20:32:00+00:00

Sunspots are familiar phenomena. Today, the regular cycle of solar activity waxes and wanes about every eleven years. No one has yet fully explained the intricate processes that fashion sunspot cycles, nor their maxima and minima. A typical minimum in the eleven-year cycle is about six sunspots, with some days, even weeks, passing without sunspot activity. Monthly readings of zero are very rare. Over the past two centuries, only the year 1810 has passed without any sunspot activity whatsoever. By any measure, the lack of sunspot activity during the height of the Little Ice Age was remarkable.

The seventeenth and early eighteenth centuries were times of great scientific advances and intense astronomical activity. The same astronomers who observed the sun discovered the first division in Saturn's ring and five of the planet's satellites. They observed transits of Venus and Mercury, recorded eclipses of the sun, and determined the velocity of light by observing the precise orbits of Jupiter's satellites. Seventeenth-century scholars published the first detailed studies of the sun and sunspots. In 1711, English astronomer William Derham commented on "great intervals" when no sunspots were observed between 1660 and 1684. He remarked rather charmingly: "Spots could hardly escape the sight of so many Observers of the Sun, as were then perpetually peeping upon him with their Telescopes ... all the world over."6 Unfortunately for modern scientists, sunspots were considered clouds on the sun until 1774 and deemed of little importance, so we have no means of knowing how continuously they were observed.

The period between 1645 and 1715 was remarkable for the rarity of aurora borealis and aurora australis, which were reported far less frequently than either before or afterward. Between 1645 and 1708, not a single aurora was observed in London's skies. When one appeared on March 15, 1716, none other than Astronomer Royal Edmund Halley wrote a paper about it, for he had never seen one in all his years as a scientist-and he was sixty years old at the time. On the other side of the world, naked eye sightings of sunspots from China, Korea, and Japan between 28 B.C. and A.D. 1743 provide an average of six sightings per century, presumably coinciding with solar maxima. There are no observations whatsoever between 1639 and 1700, nor were any aurora reported.

In the 1890s, astronomers F. W. G. Sporer and E. W. Maunder drew attention to this long sunspot-free period in the late seventeenth and early eighteenth centuries. If seventeenth-century observers were to be believed, almost all sunspot activity ceased for seventy years, a dramatic departure from the modern sun's behavior. This lacuna in sunspot activity has since been known as the "Maunder Minimum."

In later papers, Maunder made some striking assertions. First, very few sunspots were seen over the seventy years between 1645 and 1715. Second, for nearly half this time (1672-1704) no sunspots were observed on the northern hemisphere of the sun whatsoever. Only one sunspot group at a time was seen on the sun between 1645 and 1705. Last,

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