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The Spörer Minimum is a hypothesized 90-year span of low solar activity, from about 1460 until 1550, which was identified and named by John A. Eddy in a landmark 1976 paper published in ''Science'' titled "The Maunder Minimum".〔(Eddy, J. A., "The Maunder Minimum", ''Science'' 18 June 1976: Vol. 192. no. 4245, pp. 1189–1202 ), (PDF Copy )〕 It occurred before sunspots had been directly observed and was discovered instead by analysis of the proportion of carbon-14 in tree rings, which is strongly correlated with solar activity. It is named for the German astronomer Gustav Spörer.〔 (【引用サイトリンク】 url = http://www.windows.ucar.edu/tour/link=/sun/activity/sunspot_history.html&edu=high ) The Spörer Minimum (1420 to 1570), named after the German astronomer Gustav Spörer. 〕 ==History of Solar Activity== For details on solar activity see: solar variation. Solar activity is conventionally expressed in the form of sunspot counts, but this measure is only reliable for periods after records of sunspot observations were routinely made by western astronomers. For periods before sunspot records, solar activity can be found from proxy methods, most notably the production of radioisotopes in the Earth's atmosphere from interaction with cosmic rays, which are modulated by the solar activity.〔Ilya G. Usoskin, ''A History of Solar Activity over Millennia,'' section 3, ("The Proxy Method of Past Solar-Activity Reconstruction" ), ''Living Reviews in Solar Physics'', 2013 (accessed 21 July 2015)〕 The Carbon-14 method used by Spörer to identify the minimum makes use of the fact that high solar activity is correlated with low production of carbon-14 in the atmosphere. Wilfried Schröder published a table of observed aurora borealis during the Spörer Minimum which showed that the solar cycle was active〔Wilfried Schröder, ''Annals Geophys.'', 1994〕 Miyahara ''et al.'' likewise found the 11-year solar cycle was still prominently detected in the carbon-14 record even during the minimum. The amplitude of the 11-year cycle seems to have been modulated only for the period around 1455-1510 A.D. 〔Miyahara, H., Masuda, K., Muraki, Y., Kitagawa, H. and Nakamura, T., 2006a, “Variation of solar cyclicity during the Spoerer Minimum”, J. Geophys. Res., 111(A10), A03103. (abstract ) (accessed 12 July 2015)〕 Jiang and Xu look at sunspot records and aurora sightings from China during the period, and suggest that a minimum from 1450-1560 is specious. They suggest dates for the sunspot minimum of 1400-1510.〔Yaotiao Jiang and Zhentao Xu, "On the Spörer Minimum", ''Astrophysics and Space Science,'' Jan. 1986, ''Vol. 118'', 1-2, pp 159-162. (Abstract and link ) (accessed 12 July 2015)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spörer Minimum」の詳細全文を読む スポンサード リンク
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