334 HOW TO OBSERVE THE HEAVENS. 



visible at all seasons, and in all northern latitudes, are necessarily familiar to 

 every eye, they may serve as standards or moduli by which the astronomical 

 amateur may estimate the different orders of magnitudes of the stars generally. 

 One of the most convenient methods of ascertaining and identifying the 

 principal stars on the heavens which the amateur observer can adopt, consists 

 in selecting other known stars as pointers. We shall explain this method by 

 one or two examples. In the constellation of Ursa Major, there are besides 

 the seven stars above mentioned, five others of the third magnitude, which are 

 marked 3 h * ^ *P> in the annexed diagram. 



To find and <, fig. 2, let the observer imagine a straight line drawn from & to 

 0, to be continued beyond /? The first stars of the same magnitude as <5 which 

 it will meet will be and < Again, let a straight line be imagined to be drawn 

 fromJtoy,and continued beyond y- It will carry the eye to the star ^ of the 

 same magnitude as t. Finally, if a line be imagined to be drawn from d per- 

 pendicular, the line passing through the four stars <*, , o, and <> it will conduct 

 the eye to the two stars * and /*. 



If the observer look at any good map of the stars,* he will find that the 

 stars , P, and y, are on the body of the figure of the Bear ; <5, , , ;, form the 

 tail, o and l are on the right fore leg, ^ on the hinder right thigh, and A and /* 

 on the hinder right paw. 



The practical usefulness of the imaginary figures which give names to the 

 constellations will thus be understood. If we desire to express the position 

 of the star i Ursa Majoris, for example, we say that it is at the tip of the tail 

 of the Great Bear. 



The seven principal stars of this constellation being all less than forty de- 

 grees from the north pole, will be always above the horizon in latitudes greater 

 than forty degrees. Hence it is that this constellation is so familiarly known. 

 It is in the quarter of the heavens opposite to that in which the sun is in the 

 month of March, and is therefore visible at midnight near the meridian above 

 the pole at that season. In the month of September it is visible at midnight 

 below the pole. 



The point in the firmament whose position ought to be most familiar to the 

 observer is the pole. Its position is marked by a star of the second magnitude, 

 which is so near to it that the interval can not be appreciated without the use 

 of good astronomical instruments. It is therefore very important that an easy 

 method, applicable without instruments, should be available for the discovery 

 of this star. The method already explained may be used also in this case. 

 In the annexed figure the seven stars of Ursa Major are represented in the 

 lower part. The stars of the upper part are those of a constellation near the 

 pole called Ursa Minor. The actual position of the pole is represented at 0; 

 and the star immediately above it is the pole-star. 



If a line be conceived to be drawn between the two stars and 0, fig. 3, in 

 Ursa Major, and continued beyond , it will pass very nea'rly through the pole- 

 star, and as there is no star of the same magnitude near the latter, the eye 

 can not fail to recognize it. The other stars of the constellation of the lesser 

 Bear, are all of inferior brightness. The figures annexed to the several stars 

 in this diagram express their respective magnitudes. The two stars and 0> 

 of Ursa Major, have hence been denominated the POINTERS. The apparent 

 distance between the pointers is 5, while the distance from to the pole-star 

 is 29. Thus the latter distance is nearly six times the former. 



* We should recommend the amateur astronomer to be provided with the maps of the stars pub- 

 lished on extremely cheap terms by the London Society for the Diffusion of Useful Knowledge, t<* 

 gether with the " Companion to the Maps," by Professor de Morgan. These are always on hand 

 at Mr. Baldwin's bookstore, Broadway, New York. 



