Page:Popular Science Monthly Volume 92.djvu/252

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��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.

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