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HOW TO OBSERVE THE HEAVENS. 



Example 3. — To find the point at which * Aquila passes the meridian of 

 New York. 



The distance of a Aquila north of the celestial equator being taken fr«m the 

 map to be 28°. 45', we shall 



From - 40°. 43' 

 Subtract - 28°. 45' 



11°.58' 

 and the remainder, 11°. 58', will be the distance south of the zenith at which 

 the star passes the meridian.* 



A celestial globe, where it can be had, will prove a ready and convenient 

 aid to the amateur in astronomy, superseding the necessity of many calculations 

 which are often discouraging and repulsive, however simple and easy they 

 may be to those who are accustomed to such inquiries. Most of the almanacs 

 contain tables of the principal astronomical phenomena, of the places of the 

 sun and moon, and of the principal planets as well as the times when the 

 most conspicuous stars are on the meridian of Washington after sunset. These 

 data, together with a judicious use of the globe and a tolerable telescope, will 

 enable any person to extend his acquaintance with astronomy, and may even 

 enable him to become a useful contributor to the common stock of information 

 which is now so fast increasing by the zeal and ability of private observers in 

 so many quarters of the globe. 



To prepare the globe for use, let small marks (bits of paper gummed on will 

 answer the purpose) be placed upon it, to indicate the positions of the sun, 

 moon, and planets, at the time of observing the heavens. The place of the 

 sun on the ecliptic is usually marked on the globe itself. If not, its right as- 

 cension (that is, its distance from the vernal equinoctial point, measured on the 

 celestial equator), and its declination (that is, its distance north or south of 

 the equator), are given in the almanac for every day. The moon's right 

 ascension and declination are likewise given. f 



To find the place of an object on the globe when its right ascension and dec- 

 lination are known. 



Find the point on the equator where the given right ascension is marked. 

 Turn the globe on its axis till this point be brought under the meridian. 

 Then count ofF an arc of the meridian (north or south of the equator, according 

 as the declination is given), of a length equal to the given declination, and the 

 point of the globe immediately under the point of the meridian thus found, will 

 be the place of the object. By this rule, the position on the globe of any 

 object of which the. right ascension and declination are known, may be im- 

 mediately found, and a corresponding mark put upon it. 



To adjust the globe so as to use it as a guide to the position of objects on \ 

 the heavens, and as a means of identifying the stars and learning their names, 

 let the lower clamping-screw of the meridian be loosened, and let the north \ 

 pole of the globe be elevated by moving the brass meridian until the arc of this i 

 meridian between the pole and the horizon be equal to the latitude of the place \ 

 of observation. Let the clamping-screw be then tightened so as to maintain the < 

 meridian in this position. Let the globe be then so placed that the brass me- \ 

 ridian shall be directed due north and south, the pole being turned to the i 

 north. This being done, the globe will correspond with the heavens so far as < 

 relates to the poles, the meridian, and the points of the horizon. 



• In these examples I have taken the declinations roughly from the map rather than from the ( 



tables, as that would be the method which an amateur would probably use. I 



t In the United States Almanac a sufficient collection of tables and astronomical data for all } 



the purposes of the amateur astronomer are given. It will be necessary that he should first render ( 



himself familiar with the abbreviations and symbols, after which he will find the greatest advantage < 



from that work. ( 



