Monday, June 16, 2008

One Hundred Million of Stars


Let us see what richness of stellar distribution is implied by this number of 100,000,000 of visible stars. It may be easily shown that the area of the whole sky in both hemispheres is 41,255 square degrees. This gives 2,424 stars to the square degree. The moon's apparent diameter being slightly over half a degree — 31 minutes 5 seconds — the area of its disk is about one-fifth of a square degree. The area of the whole star sphere is consequently about 200,000 times the area of the full moon. A total of 100,000,000 of stars gives, therefore, 500 stars to each space of sky equal in area to the full moon.

This seems a large number, but stars scattered even as thickly as this would appear at a considerable distance apart when viewed with a telescope of a high power. As the area of the moon's disk contains about 760 square minutes of arc, there would not be an average of even one star to each square minute. A pair of stars half a minute or 30 seconds apart would form a very wide double star, and with stars placed at even this distance the moon's disk would cover about 3,000, or six times the actual number visible in the largest telescopes. — Gentleman's Magazine.

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