POPULAR ASTRONOMY 



325 



Evening Sky Map for December. 



BY PROF. ALFRED MITCHELL, OF COLUMBIA 

 UNIVERSITY. 



On one of the cool crisp evenings 

 that come at this season of the year, 

 we see the heavens sparkling with 

 countless gems of light, apparently mil- 

 lions in number. Indeed, most people 

 believe that it would be absolutely im- 

 possible to count all the stars that can 

 be seen with the naked eye ; and 

 throughout all ages of the world's lit- 

 erature, the terms "numberless as the 

 sands of the sea shore," and "count- 

 less as the stars," have been regarded 

 as synonymous. But to be "like the 

 stars in number," would not necessi- 

 tate a very great number, if one refers 

 in that, to the stars that may be seen 

 with the naked eye. As a matter of 

 fact, we could not count these stars up 

 into the millions, nor even to hundreds 

 of thousands, nor yet to tens of thou- 

 sands. At any one time only three 

 thousand stars can be seen without a 

 telescope by any observer, and in the 

 whole heavens there are less than six 

 thousand stars that may be seen with 

 the naked eye. 



Even with a small telescope, the 

 light gathered to fall on the retina of 

 the eye is many times that which falls 

 on the unaided eye, and as a conse- 

 quence many more stars are revealed. 

 With greater and greater telescopes 

 there are brought to our ken, fainter 

 and fainter stars. Strange as it may 

 seem, a moderate-sized photographic 

 telescope with the modern sensitive 

 plate can portray stars and nebulae 

 which are too faint to be seen by the 

 keen eye of the astronomer using even 

 the great forty-inch Yerkes telescope. 

 It has been estimated that the photo- 

 graphic plate has revealed no less than 

 one hundred million stars. Each of 

 these stars shines by its own light and 



is, consequently a sun. How would 

 our own sun compare in size and bril- 

 liancy with one of these distant orbs 

 of light? Do some of these suns have 

 planets circling about them? Do any 

 of these planets (if there are such) re- 

 semble our own earth? Are they in- 

 habited? These are interesting ques- 

 tions that we can partially answer. 



The Darwinian theory of evolution 

 explains the gradual development of 

 life on this mundane sphere of ours. 

 In the heavens, we see abundant evi- 

 dences of evolution, changes going on 

 with majestic slowness, through eons 

 of time. In the evolution of these hun- 

 dreds of millions of other suns, it does 

 not seem impossible for some to have 

 developed like our own sun, nor does 

 it seem unthinkable for some of the 

 planets belonging to these solar sys- 

 tems even to be inhabited. Different 

 environment would have made men on 

 these planets different from the aver- 

 age American, but none the less they 

 may be human beings. It seems hard- 

 ly likely that the vast universe was 

 made solely for our pleasure, with 

 stars and other systems serving no 

 other useful purpose than being mere 

 points of light in the sky. 



To compare the brilliancy of our 

 own sun with others, we must know 

 the relative distances and their rela- 

 tive brightness. The brightest fixed 

 star in the heavens is the brilliant dog 

 star Sirius, which is found low down 

 to the southeast in the early evening. 

 The astronomer keeps track of the 

 brightness of the stars by their "mag- 

 nitudes." The brightest of them are 

 of the first magnitude, those just visi- 

 ble to the naked eye of the sixth mag- 

 nitude. The twenty most brilliant 

 stars known to the ancients were re- 

 garded as of the first magnitude stars. 

 As science became more exact it be- 



