494 



Marvels of the Universe 



objects, appear dark, sometimes very dark, through contrast with their surroundings ; the " faculae " 

 are very bright — bright even as compared with the brightest parts of the Sun's surface. The 

 " spots " appear to be exaggerations of the least brilhant interstices of the " mottling " ; the 

 " faculae " of the most brilliant ; but are so much larger, more definite and stable than the fine details 

 of the photospheric network as to make them quite distinct classes of the solar details. But the 

 gradation is complete from the largest Sunspot down to the minutest detail of the granulation, and 

 it is not always easy to distinguish between a very small, faint " pore," as the smallest spots are 

 called, and some of the larger, more distinct, of the interspaces of the " mottling." 



Spots vary much in size, appearance and history, but the type most frequently seen begins 



usually after the " photo- 

 spheric network " in some . 

 region has been observed to 

 be apparently perturbed, 

 and to take on a coarser 

 appearance than usual. 

 Then two small " pores " 

 appear near to each other, 

 and begin to grow and 

 move apart. One of the 

 two soon shows itself as 

 a round, sharply-defined 

 object, especially on its 

 advancing side, and before 

 long it becomes the leader 

 of the group, moving for- 

 ward on the Sun's surface 

 away from the rest of the 

 group, often at the astonish- 

 ing speed of three hundred 

 miles an hour. Meanwhile 

 the other member of the 

 original pair has been grow- 

 ing, possibly even more 

 quickly, but without show- 

 ing the same symmetry and 

 definiteness. The two are 

 now widely separated in 

 consequence of the rapid 

 forward motion of the 

 leader ; but new spots have broken out in the gap, and the entire group consists of a long chain, 

 the largest members of which are the original pair, now at the two ends of the chain. Then the 

 general bright surface of the Sun — the " photosphere " — which is brighter than usual, and 

 apparently piled up in front of the leader spot and on either side of the chain, begins to flow 

 over and invade, first the smaller middle spots, and then the rear spot. The accompanying 

 photograph, taken on July 31, 1906, shows a fine but short stream of spots at this stage ; the 

 small middle spots being almost hidden by this boiling over of the photosphere, while the rear spot 

 is crossed by many bridges or invaded by streams of bright photospheric material, actually rushing 

 down into its depths. In the photograph taken three daj's later this bright material has all but 

 covered tlie hinder portion of the group, while the leader spot has still retained its outline ; its 



Photoiintph laKi'ii al'] [(iret'nicich OhsertiUoni. 



SPOTS ON THE SUN. 



The larger spot is about 800 millions of square miles in area, or 32,000 miles in 

 diameter. It shows a spot in its stable condition, this spot lasting for more than three 

 months. The smaller spot is only about 1 20 millions of square miles in area, and is a 

 member of a group that lasted only a few days and changed rapidly. 



