314 GEOGRAPHY AND ASTRONOMY. Or it may be done with very little error 'by standing up- right and looking straightforward to the pole star, with a stick, or staff between your hands, then raise -up the staff' as straight as you can over-right the pole, and observe what stars it covers in that motion. But, these methods . are rude, and only serve for vulgar purposes. Problem XXXIV. " To find at what hour of any day a known star will come upon the meridian. Substract the right ascension of the sun for that day from the right ascension of the star, the remainder shews how many homy after noon the star will be on the meridian. Suppose I would know at what hour the great bear's guards or pointers will be on the meridian on the 27th of April ; (for they come always to the meridian nearly both at once.) The right ascension of the sun that day is about two hours 19 minutes. The right ascension of those stars is always ten hours 24 minutes. Sub- stract the sun's R. A. from the star's R. A the remainder is five minutes past eight o'clock at night, and at that time will the poin- ters be on the meridian. H. M. Right aseen. of pointers is - 10 24 Right aseen. of sun April 27th is 2 19 Time of night 8 5 Note, If the sun's right ascension be greater than the right ascension of the star, you must add 24 hours to the star's right ascension, and then substract as before. You may easily find also what day any star (suppose either of the pointers) will be on the meridian just when the sun is there viz. at 12 o'clock. Find in the tables of the right ascension of the sun what day that is wherein the sun's right ascension is the same (or very near the same) with that star's, which is the 28th of August. The sun's right ascension is 10 hours 28 minutes, then the sun and star are both on the noon meridian near the sanie time. But the sun's right ascension on the ;tad of Febru- ary is 22 hours 24 minutes.. Therefore the sun at that time is in the noon meridian when the star is in the midnight meridian, there being just 12 hours difference. Thence you may reckon when the star will be on the meri- dian at any time ; for about 15 days after it will beon the meridi- an at 11 o'clock, 30 days after at 10 o'clock. So that every month it differs about two hours ; whence it comes to pass that in 12 months its difference arising to 24 hours it comes to be on the me- ridian again at the same time with the sun. Problem XXXV. "'Raving the altitude of any star given to find the hour."
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