![]() This and other studies have shown that the Sun (as well as other stars) spends about a quarter of its time with very few sunspots. Data from 8,000 year-old bristle-cone pine trees indicate 18 periods of sunspot minima in the last 7,800 years (1). By means of the premise of excess 14C concentrations in independently dated material (such as tree rings), other minima have been found at times prior to direct sunspot observations, for instance the Sporer minimum from 1450 to1540. During the Maunder minimum the proportional concentration of radio-carbon ( 14C) in the Earth’s atmosphere was slightly higher than normal, causing an underestimate of the radio-carbon date of objects from those periods. There have been several periods during which sunspots were rare or absent, most notably the Maunder minimum (1645-1715), and less markedly the Dalton minimum (1795-1820) (Fig 2.8 in the book). The 11-year cycle of the number of sunspots was first demonstrated by Heinrich Schwabe (1789-1875) in 1843. In 1801 William Herschel (1738-1822) attempted to correlate the annual number of sunspots to the price of grain in London. In 1647 Johannes Hevelius (1611-87) in Danzig made drawings of the movements of sunspots eastwards and gradually towards the solar equator. Sunspots were observed in the Far East for over 2000 years, but examined more intensely in Europe after the invention of telescopes in the 17th century. There is also a superimposed fluctuation with a period of 25 months, i.e. There is a strong radial magnetic field within a sunspot, as implied in the picture, and the direction of the field reverses in alternate years within the leading sunspots of a group. The number of sunspots peaks every 11.1 years. The temperature within sunspots is about 4,600 K. The layer is about 6,000 degrees Kelvin at the inner boundary and 4,200 K on the outside. The photosphere is about 400 km deep, and provides most of our solar radiation. Sunspots have a diameter of about 37,000 km and appear as dark spots within the photosphere, the outermost layer of the Sun. Sunspots and climate Sunspots and climate ![]()
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