49^ Marvels of the Universe 



apparently elliptic form is due to the fact that the group is now seen near the edge of the Sun, and 

 is, therefore, strongly foreshortened, as it is being looked at nearly sideways. The next phase in 

 the history of a group of this tj'pe is for the whole of the hinder portion to disappear under the 

 photospheric material, leaving the leader spot alone. As an isolated round spot, it may last for 

 some weeks, or even for two or three months, without undergoing much change be\'ond a slow 

 contraction. Sometimes this process goes on mitil the spot has filled up ; at other times it 

 breaks up into a number of small fragments before its disappearance. 



This particular stream was a short one for its size, being only about fifty thousand miles in 

 length. Some groups of Sunspots have been known to stretch out to a length of nearly two hundred 

 thousand miles ; other spots, like the great one shown on the photograph taken on February 13, 

 1892, have been less drawn out and more compact, but have covered a greater total area. The 

 principal group on that photograph covered an area of three thousand five hundred millions of 

 square miles, more than eight hundred times the area of Europe ; seventy worlds as large as our 

 own could have lain side by side within its bounds. We do not know what the depth of the spot 

 was ; without doubt the depth was very shallow as compared with its area ; but this would still 

 be the case if it were some few thousands of miles deep. The actual dimensions of Sunspots are, 

 therefore, very often very great indeed, as compared with that of the earth ; worlds as large as our 

 own could He in such a spot as peas in a saucer. 



But, as compared with the Sun itself, Sunspots are very small. It is very seldom, even when 

 they are largest and most numerous, that one five-hundredth part of the Sun's surface is covered 

 by them. And as the very darkest part of the darkest Sunspot is really very bright, and the faculae 



J'/iofogn'j'ft tal>rii o.O {Greenwich Ohservatory. 



SPOTS ON THE SUN. 



A. compact stream of spots, about 50.000 miles in greatest length and 30.000 in greatest breadtK. and covering 2.300 

 millions of square miles. No fewer than fifty worlds as large as our own could lie side by side within its borders. The group is 

 [beginning to decline, and the bright material of the Sun's general surface is overflowing the following half of the group. 



