Is Solar Activity Constant?
Another fundamental question is the degree to which the 22-year cycle of solar transient activity repeats itself over long stretches of time. In 1893, E. Walter Maunder (1851-1928), a British astronomer, found in European historical records that very few sunspots were seen in the period from 1645 to 1715, now known as the Maunder Minimum. Within the last several years, Maunder’s work has been confirmed and extended by astronomers worldwide. In addition to the absence of sunspots during the Maunder Minimum, very few aurora were observed in Europe, and during eclipses, the corona was also absent or very weak. Virtually no sunspots were reported in Asia during the Maunder Minimum, even though naked-eye sunspot-sighting reports exist there from as early as 28 B.C. Finally, measurements of the amount of carbon 14 (C146), a radioactive isotope of carbon, in tree rings show that during the Maunder Minimum there was an excess of this isotope in the Earth’s atmosphere. We believe that the high-
