THE VISIBLE STARS. 



Sir William Herschel, to whose researches we are indebted for a large ror- 

 tion of the knowledge which we possess respecting the fixed stars, has inves- 

 tigated the probable progression of distances which regulate the stars visible 

 to the naked eye, and has shown reasonable grounds for concluding that the 

 smallest visible star is at a distance about twelve times greater than stars of 

 the first magnitude. He supposes that the intermediate stars between the 

 smallest that can be seen by the naked eye, and stars like the dogstar, which, 

 from their brightness, must be presumed to be nearest to us, are ranged at in- 

 termediate distances. It would therefore follow that if we assume the distance 

 of the nearest star according to the results of Bessel's observations, to be a 

 space that light would move over it in 10 years, the distance of the smallest 

 star perceivable by unassisted vision must be such that light would take 120 

 years to move over ! If, then, we imagine a sphere surrounding us, the radius 

 of which is equal to the space that light moves over in 120 years, that sphere 

 is the range of natural and unassisted vision, and is that portion of the universe 

 which men are privileged to contemplate unaided by art. 



MAGNITUDE OF THE STARS. 



The extent of the stellar universe visible to the naked eye, and the arrange- 

 ment of stars in it and their relative distances, have just been explained. But a 

 natural curiosity will be awakened to discover not merely the position and ar- 

 rangement of those bodies, but to ascertain what is their nature, and what parts 

 they play on the great theatre of creation ? Are they analogous to our planets ? 

 Are they inhabited globes, warmed and illuminated by neighboring suns ? Or 

 on the other hand, are they themselves suns, dispensing light and life to sys- 

 tems of surrounding worlds. 



When a telescope is directed to a star, the effect produced is strikingly dif- 

 ferent from that which we find when it is applied to a planet. A planet, to 

 the naked eye, with one or two exceptions, appears like a common star. The 

 telescope, however, immediately presents it to us with a distinct circular disk 

 similar to that which the moon offers to the naked eye, and in the case of some 

 of the planets a powerful telescope will render them apparently even larger than 

 the moon. But the effect is very different indeed when the same instrument 

 is directed even to the brightest star. We find that instead of magnifying, it 

 actually diminishes. There is an optical illusion produced, when we behold 

 a star, which makes it appear to us to be surrounded with a radiation which 

 causes it to be represented when drawn on paper, by a dot with rays diverging 

 on every side from it. The effect of the telescope is to cut off this radiation, 

 and present to us the star as a mere lucid point, having no sensible magnitude ; 

 nor can any augmented telescopic power which has yet been resorted to pro- 

 duce any other effect. Telescopic powers amounting to six thousand were 

 occasionally used by Sir William Herschel, and he stated that with these the 

 apparent magnitude of the stars seemed less, if possible, than with lower 

 powers. 



We have other proofs of the fact that the stars have no sensible disks, among 

 which may be mentioned the remarkable effect called the occultation of a star by 

 the dark edge of the moon. When the moon is a crescent or in the quarters, as 

 it moves over the firmament, its dark edge successively approaches to or recedes 

 from the stars. And from time to time it happens that it passes between the 

 stars and the eye. If a star had a sensible disk in this case, the edge of the 

 moon would gradually cover it, and the star, instead of being instantaneously 

 extinguished, would gradually disappear. This is found not to be the case ; 

 the star preserves all its lustre until the moment it comes into contact with the 



