THE EARTH, THE SUN, AND SUNSPOTS ^ 



By LoBiNQ B. Andrews 

 Instructor in Astronomy and Executive Secretary of the Harvard Observatory 



[With 2 plates] 



About thrice a year there lies upon my desk a letter which typi- 

 cally reads in the following fashion; "I would greatly appreciate 

 it if you could send me a list of dates of maximum and minimum 

 sunspot activity running back to around 1850. I believe I have dis- 

 covered a correlation between sunspot activity and business activity, 

 but, inasmuch as I have been unable to get the sunspot periods accu- 

 rately, I am unable to carry the correlation back over a sufficiently 

 long period of time. I would greatly appreciate any help you can 

 give me along these lines." 



This letter is the stimulus to take once again from the observatory's 

 library the volume I have so frequently fingered, the Astronomische 

 Mitteilungen of the Ziirich Observatory, to open it at no. 132, page 

 67, and to extract therefrom the list of sunspot maxima and minima 

 for as long a period of time as the writer requests. I find, for example, 

 that since 1900 there has been maximum spottedness at the following 

 times: 1906.4, 1917.6, and 1928.4; and minimum spottedness at 1901.7, 

 1913.6, 1923.6, and 1933.8. An arithmetician will inform you that these 

 figures tell of a variation of spottedness of the sun possessing a pe- 

 riod of 10.8 years, or, as one commonly states it, a period of 11 years. 

 A further perusal of the table — and it lists the maxima and minima 

 back to 1610 — reveals that this period is not reproduced with clock- 

 like precision. One notes a minimum interval of 7.3 years and a 

 maximum interval of 15.0 j^ears. In fact the long-term average for 

 the period of sunspot variation is 11.13 years. Other idiosyncrasies 

 are noted in the heights of maxima and the depths of minima. 



The average person of today is endowed with sufficient intelligence 

 to avoid looking directly at the sun without protection for the eyes. 

 Yet it was not always so. We are informed that the very early Chi- 

 nese astronomers observed the sun with the naked eye and discovered 



1 Reprinted by permission from the Harvard Aluinui Bulletin, May 1, 1036. 



137 



