John A. Eddy

John A. Eddy

John Allen "Jack" Eddy (March 25, 1931—June 10, 2009) was an American astronomer who published professionally under the name John A. Eddy but much of the content referencing him can be found under his nickname Jack which he preferred to use. In 1976 Dr. Eddy published a landmark paper in Science titled "The Maunder Minimum" where, using the Nineteenth Century works of Edward W. Maunder and Gustav Spörer, he identified a 70-year period from 1645 to 1715 as a time when solar activity all but stopped. In making the case for the anomaly, he gathered and interpreted data from a wide variety of sources, including first-hand accounts from extant historical observations of the Sun going back to the telescopic observations of Galileo and other contemporary scientists of the 17th and early 18th centuries; from historical reports of the aurora borealis observed in past centuries in Europe and the New World; from visual observations of sunspots seen with the unaided eye at sunrise and sunset in dynastic records from the Orient; from existing descriptions of the eclipsed Sun; and from measurements of carbon-14 in dated tree-rings. In the last of these, which can be used as a proxy indicator of solar activity, he found evidence of other similar periods of solar quiescence in the distant past, the most recent an even longer 90-year span, from about 1460 until 1550, which he named the Spörer Minimum. Both the Maunder and Spörer minima fell during the coldest parts of the Little Ice Age, which suggested a meaningful connection between the longer term behavior of the Sun and of the Earth’s mean surface temperature. In advancing the theory that the Sun is a variable star Eddy observed: "It has long been thought that the Sun is a constant star of regular and repeatable behavior. Measurements of the radiative output, or solar constant, seem to justify the first assumption, and the record of periodicity in sunspot numbers is taken as evidence of the second. Both records, however, sample only the most recent history of the Sun."