Marvels of the Universe 



493 



SPOTS ON THE SUN 



BY E. WALTER MAUNDER, F.R.A.S. 



" There are spots on the Sun " has passed into a proverb, with the pessimistic meaning that there 

 is no character so bright but that an attentive search can detect some slight blemish or imper- 

 fection in it. But the spots reallj' on the Sun add, without doubt, to its importance to us, and 

 certainly to its interest. 



WTiat are these spots, and what is their significance ? The Sun, as examined under good 

 conditions \\ith a telescope magnifying from one hundred to two hundred diameters, shows a very 

 briUiant surface of nearly uniform brightness. Nearly uniform, not quite ; for a close examination 

 shows that the whole is co^'ered with a very deHcate network. Everywhere there are minute 

 points of hght a little above the average in brightness ; ever3rwhere in the intervals between 

 these bright points there are dots and lines that are a little less bright than the average. A 

 photograph of the Sun, taken on a sufficiently large scale to bring out this delicate 

 structure distinctly, looks like a highly magnified picture of an irregularly woven fabric. 

 The unvarjing briUiancy of the Sun's surface, as seen by the naked eye, really covers a very 

 intricate structure, and considerable ranges of brightness ; but these are all details in high light ; 

 there is no question of real darkness on the Sun, there are only dift'erences of degree in brightness. 



In general these 

 differences are not 

 great, and might 

 even be overlooked 

 on a hasty glance, 

 oi" if the " seeing " 

 were not good ; and 

 in any case, this 

 " granulation," or 

 mottling, " or 

 " photospheric net- 

 work," as it has 

 been termed, is too 

 minute, and changes 

 too quickly in its 

 details, for much to 

 be made out from 

 it. The Sun would, 

 therefore, be a very 

 uninteresting ob- 

 ject for telescopic 

 scrutiny if larger 

 and more definite 

 features were not re- 

 cognized from time 

 to time, and such 

 features are found 

 in the " spots " and 

 the " faculae." 



The " spots," 

 though really bright 



Photograph taken aj,'\ [Oreenwich Obscrmtoru. 



SPOTS ON THE SUN. 



Photograph of the Sun taken on February 13. 1892, showing in the southern portion one of the 

 largest spots ever seen upon the solar surface. The total area of the great spot was 3.000 tnillions 

 of square miles : including the small spots close to it. the entiie area of the whole group amounted 

 to 3,500 millions. 



