When the Sun Went Strangely Quiet

Abstract

history of science contains more than a few instances in which an old idea or hypothesis, considered improbable, dubious or merely wrong by modern investigators, is, through a combination of new evidence a more thorough look at the old evidence, shown to be correct after all. Something like this seems to be happening to modern science's view of the sun. current dogma is the sun is steady, dependable, constant. In this view, its well-known 11-year sunspot cycle is the manifestation of a smoothly running, well-ordered machine, clicking with regularity like astrophysical clockwork. It is a comfortable view, the sun being of some importance to us all here on earth. Now an astronomer with a historical bent has delved back through past observational records and, by making numerous independent cross checks, resurrected made a persuasive case for an old hypothesis the solar cycle the sun itself have changed in historic time. evidence shows for a 70-year period from A.D. 1645 to 1715 sunspots were almost totally absent on the surface of the sun. Solar activity was at a near-zero level, a true strange anomaly. is totally unlike the modern behavior of the sun, says the astronomer, John A. Eddy of the National Center for Atmospheric Research's High Altitude Observatory in Boulder, Colo., and the consequences for solar terrestrial physics seem to me profound. evidence shows not only a minimum in solar activity from A.D. 1645 to 1715 but also an earlier minimum from A.D. 1460 to 1550 an even earlier maximum from A.D. 1 100 to 1250. We now have to realize, Eddy says, that the sun's behavior has been better in the last 200 years than in the previous 1,000 years. view solar activity can has varied to such a major degree in long-term patterns in historic time alters widely accepted assumptions about the constancy of the sun. We've shattered the Principle of Uniformitarianism for the sun, Eddy says. By this he means the present behavior of the sun can no longer be considered a reliable guide to the behavior of the sun in the past. Eddy's conclusions imply the often-discussed 11-year solar cycle is of far less importance concern than are longer term variations-the overall envelope of solar That patterns of solar activity have varied over historic time is interesting enough in itself. But beyond that, Eddy believes the longterm fluctuations may be due to changes in the solar constant, the total radiative output of the sun. Such an idea is of fundamental importance. Whether the solar constant may vary, once considered improbable, is now being much debated. problem has taken on new significance as solar physicists climatologists consider the possible effects of the sun on variations in earth's climate. All this becomes even more intriguing when one observes the period of near total absence of solar activity from 1645 to 1715 coincides almost precisely with the coldest point in the climatic minimum on earth we now call the Little Ice Age. As Eddy puts it, The climate curve looks a lot like the curve of variability in solar activity. Eddy described his results in a session on the sun's effects on terrestrial climate at the annual meeting of the American Association for the Advancement of Science in Boston last week (his paper will appear soon in SCIENCE). When he finished, moderator George B. Field, director of the Center for Astrophysics of the Smithsonian Astrophysical Observatory the Harvard College Observatory in Cambridge, turned to the small but crowded lecture room said, Maybe we've heard a turning point in the history of science. main contribution of Eddy's analysis is to show the prolonged sunspot minimum beginning in the 17th century is not an artifact of incomplete or spurious data but is in fact real. This has been the major stumbling block to acceptance of the idea, which has been around since at least the late 19th century. It was then two well-known solar astronomers, Gustav Sporer of Germany in papers published in 1887 1889 E. W. Maunder of the Greenwich Observatory in more detailed papers published in 1890 1894, called attention to the 70-year absence of sunspots. Maunder emphasized