114 SYDNEY CHAPMAN^ B.A., D.SC.;, F.K.A.S., ON 



directly from observation, but have been calculated from the 

 numbers higher up, by a simple mathematical formula, and from 

 this it appears that the stars between the 17th and 18th magni- 

 tudes would only give an amount of light equal to ten standard 

 stars, and that the whole mass of stars fainter still would be 

 barely equal to twelve of the 1st magnitude. Tlius the total 

 light of all stars, seen and unseen, would, it appears from this 

 table, come to about that of 700 typical stars of the 1st magni- 

 tude. It has already been mentioned that half the stars are 

 feinter than the 23rd or 24th magnitude, but their total light, 

 though they number several hundred millions, does not equal 

 the light of a single 1st magnitude star. Perhaps that single 

 consideration gives as good an idea as we can possibly form of 

 their almost unimaginable faintness. 



But the table reveals another curious circumstance. The 

 stars visible to the naked eye render to us only aljout one-fourth 

 the total amount of starlight. If, therefore, all the stars that 

 we can discern individually by our unassisted sight were blotted 

 out, the total amount of starlight would only be diminished by 

 one-quarter. The midnight sky would not be seriously less 

 luminous than it is at present, though it is needless to say its 

 beauty and interest would suffer woefully. 



The light which the stars send to us can be measured in 

 another way by comparing it with the light of the full moon. 

 It is, of course, clear to everyone that when there is a full 

 moon the night is much lighter than when there is no moon at 

 all, and we are dependent simply upon the light of the stars. It 

 has been calculated that the total light of all the stars is only 

 one-hundredth that of the full moon. Or the total starlight 

 may be compared to the light of an ordinary electric lamp 

 of 16 candle-power placed at a distance of from 45 to 

 50 yards. Such a lamp would give us as much light as we 

 receive from all these many millions of stars put together. 



But the light of the stars does not reach us with the 

 uninteresting homogeneity which characterizes the light from 

 the ordinary electric lamp. The starlight is differentiated not 

 only in direction and colour but in many other ways, and from 

 these variations, as we learn to interpret them better, we shall 

 gain more and more knowledge of the stellar universe. It is 

 this tiny stream of light, though in its brightness it is only 

 (Mpial to that of an ordinary 16 candle-power lamp, placed at a 

 distance of 45 yards, that has furnished us with all the know- 

 ledge of the heavenly bodies which we possess. It is to this 

 that we owe the profound influence which astronomy has 



