284 «EOGRAPHY AND ASTRONOMY. movethe globe and the quadrant ofaltitude backward or forward, till the centre of that star meet the quadrant of altitude in the degree of altitudewhich is given, then the index will point to the true hour. Note, These three last problems being well understood, will shew you how to find at what hour any star will rise or set any day of the year ; what stars are or will ba upon the north and south meridian at any hour given ; what stars are in the east or the west, or on any points of azimuth at any time of the night ; and what altitude they have at that hour, or at that azimuth. ProblemXXXVI. " To find the latitude and longitude of any star: Also its-right ascension and declination." Put the centre of the quadrant of altitude on the proper pole of the ecliptic, whether it be north or south ; bring its graduated edge to the given star ; then that degree on the quadrant is the stat's latitude ; and the degree cut by the quadrant on the eclip- tic is the star's longitude. Thus the latitude of Arcturus is 31 degrees north : Its longitude is 200 degrees from the point aries, or 20 degrees from libra. The latitude of Sirius or the Dog Star is near 40 degrees of south latitude, and its longitude is about 100 degrees front aries, or 10 degrees from cancer. Tp find a star's right ascension and declination, see problem XVII. for it is done the same way as that of the sun ; only observe this difference, that the sun changes both his right ascension and his declination every day, whereas the fixt stars have the same right ascension and declination all the days in the year. Remember also; that the fixt stars every day in the same year, keep the same longitude and latitude, as well as the same right ascension and declination ;it but the planets are ever chang- ing all these, and the learner can know none of them but by some almanacks which are calléd Ephemerides, or tables which are calculated on purpose to shew the longitude, and latitude, or the place of the several planets among the twelve signs of the zodiac every day in the year. ProblemXXXVII. " To findthe place of any planet on the globe : Also to find at what hour any planet, (suppose Jupiter) will rise or set, orwill be upon the meridian any given day of the yeas. You must first find out by some ephemeris, what degree of what sign Jupiter possesses that clayof that year : Mark that point on the ecliptic either with chalk or with a pencil, or by sticking on * The insensible changeof the longitude, right ascension, and declination of the fixt stars, made by their Mow motion parallel. to'the ecliptic is not worth notice in this placee
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