Spoerer law states that the latitudes at which sunspots appear on the surface of the sun gradually change from latitudes in between 30-40° north and south of the sun´s equator at the beginning of a solar cycle to latitudes in between 5-10° at the end of a solar cycle. This tendency in sunspot variation was first discovered by Richard Christopher Carrington; however, Carrington´s observations were expanded later by Gustav Spoerer.
Gustav Spoerer was a German astronomer born on October 23, 1822. He is remembered for his research on sunspots and sunspot cycles. Spoerer stated in his law of spot-zones how in the greater part of the sunspot cycle there was one zone of sunspots in each hemisphere at or near the beginning of the sun´s minimum when sunspots were approaching the equator and new sunspots were appearing at higher latitudes from the equator. It is this particularity which spoerer´s law is intended to illustrate.
Spoerer along with Richard Christopher Carrington made independent discoveries of some solar features. Spoerer added to Carrington’s observations of sunspot drift and is sometimes credited for the discovery of the differential rotation of the sun based on sunspot motion. Observations made by Gustav Spoerer concerning these variations sometimes give him the credit for the discovery which shows that sunspots may be expected to be separated into two zones in either hemisphere. Spoerer´s law predicts the variation of sunspot latitudes during the stage of a solar cycle. The following explains what is Spoerer´s law?
At the beginning of a sunspot cycle, sunspots appear at the 30-45° latitudes on the sun´s surface. As the cycle progresses, sunspots tend to appear gradually at lower latitudes, until they reach the 15° latitudes, when the sun has reached it solar maximum. From this stage, sunspots continue descending lower reaching 7° at the end of the 11 year sunspot cycle. At the beginning of the next 11 year sunspot cycle, sunspots start to appear at high latitudes. Spoerer’s law can be better comprehended in a butterfly diagram.
In addition to his discoveries in relation to the sunspots variation, he made other important contributions to astronomy. Spoerer was the first to notice an unusual period of sunspot activity during the lapse years of 1645-1715 known as the Maunder minimum. Spoerer minimum is a time of low solar activity in the years 1460 to 1550 identified by astronomer John A. Eddy, who named it after Gustav Spoerer.
Gustav Spoerer studied mathematics and astronomy at the University of Berlin. He worked as a school teacher and began his observation on the sun´s features at the age of 36. Spoerer was invited to join the Potsdam Astrophysical Observatory where he was named chief observer in 1882. Spoerer retired from Potsdam in 1894. After having enjoyed perfect health throughout his entire life, he suddenly died on July 7, 1895.