THE STARRY HEAVENS IN APRIL 



373 



Virgo, may at first appear to be a 

 rather vacant region, but if it is stud- 

 ied on a dark night, and especially if 

 it is examined with a pair of opera 

 glasses, it will be found to be a region 

 of wonderful beauty. Above the beau- 

 tiful swarm of stars already referred 

 to there is a region of equally delicate, 

 though less numerous stars, which 

 form the constellation of the Hunting 

 Dogs. Two of the stars of this little 

 group (marked A and B in Eigure I) 

 are far brighter than any of the others ; 

 these are the two Dogs, Chara and As- 

 terion, held by Bootes in his "leash of 

 sidereal fire." 



plicated spiral and knotted structure 

 of the nebula very clearly. 



It is the belief of most astronomers 

 that such nebulas are great clouds in 

 the depths of space, composed of mete- 



A Wonderful Pair of Suns. 



Asterion, at B, Figure, i, is a beauti- 

 ful double star whose two components 

 are described as being white and lilac 

 colored, respectively. These two 



strange suns are drifting through the 

 depths of space together and are there- 

 fore known to be physically connected, 

 just as the earth and moon are con- 

 nected, but the path which the smaller 

 sun pursues about its giant neighbor 

 is so very large and it is moving so 

 slowly along this great path that no 

 change in its position has been certain- 

 lv detected from the careful measures 

 of the past sixty years. Certainly tens 

 of thousands of years will be occupied 

 by it in making each of its revolutions. 

 Truly a majestic and impressive celes- 

 tial svstem ! 









• ^ '-. 1 * .•'*■'■•-« •. .. • 



Spiral Nebulas. 



At the point C, below the end of the 

 handle of the Great Dipper, there is a 

 very remarkable spiral nebula, while at 

 the point D there is a pair of these 

 singular objects, and at E and F there 

 are still others. Even in a moderately 

 large amateur's telescope, however, 

 none of these really wonderful objects 

 would appear otherwise than as a very 

 faint, misty patch of light, and in such 

 a glass the nebula at F would probably 

 be wholly invisible. 



It was not until after the invention 

 of photography that the true structure 

 of these very difficult objects was 

 clearly seen. Figure 2 is from a photo- 

 graph of the nebula at F, obtained by 

 exposing a delicate photographic plate 

 for several hours to this part of the 

 sky, and it shows the extremely COm- 



Figure 2. — Photograph of the Spiral Nebula at the 

 point F, Figure 1. 



eric material, cosmic dust, gases, and 

 matter in a radiant condition, and that 

 they are very slowly shrinking to- 

 gether under the influence of their own 

 gravity. If this is true, the principal 

 part of a nebula, such as that in Figure 

 2, will accumulate at the center, form- 

 ing there a great central sun, while 

 many of the knots and condensations 

 which we see on the spiral arms will 

 ultimately become worlds, more or less 

 like our own, revolving about the 

 immensely larger central body. 



An alternate theory, held by some 

 astronomers, is that the spiral nebulas 

 are really universes of stars, almost 

 infinitely far away from our own Milky 

 Way clusters of which our sun is a 

 part. While the general appearance 

 of the photographs of these nebulas 

 may perhaps lead one to doubt the 

 reasonableness of this second theory, 

 yet it is by no means a wholly impos- 

 sible one, and in fact, much evidence 

 can be brought forward in its favor. 



If in the course of one or a few cen- 

 turies any motion or change in one of 

 these nebulas shall be definitely de- 

 tected, however, this will at once dis- 

 pose of the second theory, for evidently 

 the time required for perceptible 

 motion in an almost infinitely distant 

 stellar universe must be reckoned in 

 millions of years. And in case it is 

 thus established that these objects are 

 in and part of our Milky Way cluster, 



