440 ASTRONOMY. 



as the planets do. They appear of an infinite va- 

 riety of sizes ; yet, for convenience, it is usual to 

 class them into six or seven magnitudes: thus, 

 they are called stars of the first, second, &c. mag- 

 nitude. To the naked eye they appear innumerable ; 

 but this is only the consequence of their being scat- 

 tered in so confused a manner, and our not being 

 able to see them all at one view. The whole num- 

 ber of stars visible to the naked eye is about 3186. 

 But seldom above one-third of that number can be 

 seen by most people. From the earliest ages they 

 have been divided into groups, or constellations, 

 which have been called by the names of various 

 animals and objects, from a supposed resemblance 

 to them : such as the Great Bear, the Little Bear, 

 the Swan, &c. 



The fixed stars are placed at a distance from us 

 so great, that it cannot be ascertained by any means 

 yet known; hence, they must shine by their own 

 light, and not by the light which they receive from 

 our sun, as the planets do. Though it has been 

 formerly mentioned that the relative situations of 

 the fixed stars do not vary, yet, in the course of 

 several ages, some variations have been observed 

 among them. Some of the larger stars have not 

 the same precise situations that ancient observations 

 attribute to them, and new stars have appeared, 

 while some others which have been described, are 

 now no longer to be found. Some stars are like- 

 wise found to have a periodical increase and de- 

 crease. Others of the fixed stars, upon examination 

 with the telescope, are found to consist of two. 



Besides the phenomena already mentioned, there 

 are many luminous spots like faint bright clouds, 

 which are always seen in the same relative situation. 

 These spots are called nebulcc. When examined 



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