Air

Abstract

First spotted by Asian astronomers (with naught but their naked eyes!) in 1077, sunspots were generally ignored by western astronomers until Galileo Galilei observed them through his telescope around 1611, since soon after which time they have been surveyed more or less continuously. A German apothecary and amateur solar observer, Heinrich S. Schwabe, suspected from his observations over the years 1826 to 1837 that the number of spots on the solar disk varies regularly, and possibly periodically, with time (Schwabe 1838). Some years later he caused a stir by confirming that sunspots come and go over a cycle lasting 10 years (Schwabe 1843, 1844). He came to this conclusion simply by plotting the average number of sunspots seen each year. It seems that professional astronomers, believing the Sun to be constant, had never bothered trying this elementary exercise. Schwabe’s work came to the attention of another German, J. Rudolf Wolf. On the basis 150 years of sunspot records, Wolf established an average period of 11.1 years, although he noted considerable variations in period length and amplitude (e.g. Wolf 1858).

The climate of any point on the earth’s surface depends on a complex of factors, some of them due to influences arriving from outside the earth, and others purely terrestrial.

C.E.P. Brooks (1922, p. 15)