326 



THE GUIDE T< ) NATURE 



came necessary to distinguish between 

 these brighter stars, for some were 

 much brighter than others, and so 

 measures were made to determine the 

 brightness. The stars were compared 

 among themselves or with the light of 

 a standard candle by an instrumenl 

 called a photometer. A very exact 

 part of astronomy thus has arisen. 

 The magnitude of the stars, as a re- 



than one, by decimals, or even by neg- 

 ative numbers. Sirius is of the — 1.4 

 magnitude, Vega of 0.2 magnitude. A 

 star of the first magnitude is five mag- 

 nitudes brighter than one of the sixth, 

 and it gives just 100 times as much 

 light. The fifth root of 100 is 2.512, 

 and consequently a star of a certain 

 magnitude gives 2.512 times as much 

 light as one of a magnitude fainter. 



Evening SkyMap for December 



Dec. moon Phases 



NEW MOON Dec. I 

 FIRST Qtr Dec, 3 

 FULL MOON Dec, 16. 

 I AST Qtr. Dec. 25 

 NEWMOON.Dec.3 



Columbia 

 Universe 



MAP 



9PM.1? 

 8PM 154 

 7PM3l'i 



FACE SOUTH AND 

 HOLD THE MAP OVLR 

 YOUR HEAD-THE TOP 

 NORTH. AND YOU WILL SEE 

 THE STARS AND PLANETS 

 JUST AS THEY APPEAR 

 IN THE HEAVENS. 



SOUTH 



3 



suit of these measures, can be more 

 accurately stated. The brighter a star 

 is, the smaller the number represent- 

 ing its magnitude, and consequently a 

 star of the first magnitude is one mag- 

 nitude brighter than one of the second. 

 And one of the second magnitude is 

 two magnitudes brighter than one of 

 the fourth. In the same way stars 

 brighter than the first magnitude can 

 be representetd by numbers smaller 



(Those who understand logarithms 

 will see at a glance that log 2.512 is 

 equal to 0.4.) 



Our sun is a star of the — 26.5 magni- 

 tude, and it gives us 10,000,000,000 

 times as much light as Sirius. If the 

 sun were twice as far away from us 

 as it is, it would give only one-quarter 

 as much light. If it were 100,000 times 

 farther off than it is, its light would 

 be the same intensity as that of Sirius. 



