ASTRONOMY. 



A STRONOMY teaches whatever is known of 

 ,/x the heavenly bodies. The earth itself it 

 regards only as one of them viewing it as an 

 entire body, such as it would appear were we to 

 behold it from a sufficient distance. 



The subject falls naturally under two general 

 heads : i st, A description of the heavenly bodies 

 the aspect of the heavens as a whole ; the 

 distances, shapes, and magnitudes of the several 

 bodies ; the figures they describe in their motions ; 

 the way in which they are grouped into systems, 

 &c. zd, Physical Astronomy, or the nature of 

 the powers or forces that carry on the heavenly 

 motions, and the laws that they observe. The 

 processes of calculating the motions from a know- 

 ledge of the laws, with a view to turn them to the 

 use of man, and the management of mathematical 

 instruments for taking the necessary observations, 

 form the art of the practical astronomer; into 

 which we cannot enter. 



GENERAL APPEARANCES OF THE HEAVENS. 



When we raise our view to the sky over our 

 heads, we find it occupied with the sun by day, 

 and the moon and stars by night The sun is 

 evidently never at rest, but is either ascending 

 upwards in the sky from the east, or else sinking 

 towards the horizon or sky-line in the west, where 

 his body goes out of sight. The same continual 

 motion of rising and setting is observed in the 

 moon and in the stars. If, at the beginning of a 

 winter-night, we fix our attention on a conspicuous 

 star near the east point of the horizon, and con- 

 tinue to observe it, we shall see it rising higher and 

 higher for about six hours ; it will then begin to 

 descend to the west, and in about six hours more 

 it will reach the west point of the horizon, and 

 disappear. If we commence our watch again on 

 the following night, we may discover the same 

 star rising at the east point at about the same 



hour, and going through its course of mounting, 

 crossing, and descending the sky as before. 



If we turn to some point between east and north, 

 and notice a star just rising, we find it gradually 

 ascending in the heavens up to a certain point; 

 then descending to the west, and going out of 

 sight ; and finally reappearing in the east in about 

 twenty-four hours from the time of its previous 

 rising: but these twenty-four hours, instead of 

 being spent one half above and the other half 

 below the horizon, as in the former case, will be 

 unequally divided between the presence and the 

 absence of the star ; more than twelve hours will 

 be taken to pass from the rising to the setting, 

 and less than twelve hours will elapse between the 

 setting and the next rising. The further north the 

 point of rising, the longer the time spent in the 

 upper course, and the shorter the time in the under 

 and unseen course. If we go to the north point 

 itself, and observe a star just a little above the 

 horizon, we shall find that it will spend the first 

 twelve hours in ascending to its highest point in 

 the heavens, and the next twelve in descending to 

 the neighbourhood of the horizon ; and it will not 

 go beneath at all, but commence again to rise and 

 describe a circle in the heavens as before ; such a 

 star, therefore, will be always in sight. In like 

 manner, all stars in the north quarter lying with- 

 in the circle described by this never-setting star 

 will perform their daily movement above the 

 horizon.* 



Poles, Axis. In the inside of these circling 

 motions we may observe a point in the sky which 



In the foregoing and in succeeding paragraphs, it is supposed 

 that the stars may be seen day and night. By the naked eye no 

 star can be seen while the sun is up, but they are all in their places 

 nevertheless. The intense light of the sun generally makes other 

 celestial objects invisible. With good telescopes, however, the 

 stars may be seen in the daytime, in a clear day, except in the 

 sun's immediate neighbourhood. From the bottom of deep welU 

 and mines the stars in the sky overhead are seen through the day. 

 When the moon is at a considerable distance from the sun, it may 

 be seen when the sun is up. 



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