236 



Popular Science Monthly 



Size of Canopus (largest star known) compared with sun and earth. Canopus has a diameter 

 139 times greater than the sun's, and sun's is 109 times the earth's. How little we are! 



inquisitive mind asks: — How large is the 

 biggest star known? After years of 

 tedious and elaborate work, astronomers 

 have found that the southern hemisphere 

 possesses a star, called Canopus, which, in 

 point of size, certainly surpasses that of 

 any star yet discovered. It is an appalling 

 object. Although only a fraction of a 

 magnitude less in brightness than the 

 brightest star Sirius, it nevertheless occu- 

 pies a "back seat" in the heavens. Its 

 distance cannot be less than a hundred 

 times that of the nearest bright star 

 Alpha Centauri, which is similar in ap- 

 parent brightness. Thus we have two 

 stars of the first magnitude but situated 

 in vastly different places in the universe. 

 The rays of light which we are to-day re- 

 ceiving from (>anopus were propagated 

 from this giant sun in the fifteenth cen- 

 tury. Dwellers on this earth of ours 

 about 450 years hence will see it as it is at 

 the present moment. 



In Canopus we have a traveling 

 celewtial furnace, emitting 50,000 times 

 more light than does the sun. Its motion 

 through space amounts to something like 

 1,000 miles every minute. Its stupendous 

 diameter is 139 tirhes that of the sun's. 



being equivalent to over 120,000,000 

 miles. Its outer layers are composed 

 chiefly of glowing hydrogen. Not im- 

 probably its entire structure, right to the 

 core, represents an incandescent gaseous 

 globe, a remark which may apply equally 

 well to the majority of stars. 



We cannot conceive conditions under 

 which matter could exist near the center 

 of such a huge body. On our miniature 

 earth, for instance, pressure due to gravi- 

 tation in the oceans, amounts to the re- 

 spectable figure of seven tons every 

 square inch. If now we consider a globe 

 the size of Canopus to be constituted of 

 material having a mean density equal to 

 that of water, at the center of such a globe 

 there would be the pressure of a column 

 of water upwards of 60,000,000 miles in 

 height, besides the corresponding enor- 

 mous pull of gravitation. If we regard 

 this pressure in terms of terrestrial gravi- 

 tation it reaches over 67,000,000 tons per 

 square inch. Furthermore, we have the 

 inconceivable heat to contend with at the 

 center of such an enormous body, which 

 must be greater proportionally than at its 

 surface, just as the earth's heat is greater 

 at its center than at its surface. 



