. Mathematics, compiled from the best authors and intended to be the text-book of the course of private lectures on these sciences in the University at Cambridge [microform]. and at the time, when it is in that point,the star sets acronically. PROBLEM XVII. Given the latitude of the place, the obliquity of the ecliptic, theright ascension, and declination of a star ; to find its heli-acal rising, and setting. Note. The heliacal rising of a star is its emergencefrom the suns beams, or its first appearance above the hov-Vol. II. Oo» 490 MATHEMATICS. izon before sunrise. And the heliacal setting
. Mathematics, compiled from the best authors and intended to be the text-book of the course of private lectures on these sciences in the University at Cambridge [microform]. and at the time, when it is in that point,the star sets acronically. PROBLEM XVII. Given the latitude of the place, the obliquity of the ecliptic, theright ascension, and declination of a star ; to find its heli-acal rising, and setting. Note. The heliacal rising of a star is its emergencefrom the suns beams, or its first appearance above the hov-Vol. II. Oo» 490 MATHEMATICS. izon before sunrise. And the heliacal setting of a. star is itsimmersion in the solar beams, or disappearance near the hor-izon after sunset, on account of the proximity of the stars differ in magnitude or splendor, they rise or set he-liacally, when the sun has different degrees of depression be-low the horizon. The depression allowed is 5° ior the J ,5°for J, 10° for §, 10° for 2/, 11° for S, 11° for k, 12*for stars of the first magnitude, 13° for stars of the secondmagnitude, 14° for those of the third, 15° for those of thefonrtb, 16° for those of the fifth, and 17° for those of thesixth. T. Let •%: be the stars placewhen rising; draw the par-allel circle cd, at the requi-site distance below the hor-izon HO, the equinoctialEQ, and the ecliptic IL,by means of the stars ob-lique ascension. And des-cribe the vertical circleZqN through Z, G, thepoint where IL intersectscd, and N. In the right-angled spheric triangle BC©, (which in thisfigure is very small) C© is given ; CBO, the angle theecliptic makes with the horizon, being equal to the supple-ment of the ZCB=^, may be found by means of the triangleCBr^, in which BC^ is the co-latitude, C r, B the obliquityof the ecliptic, and C=^ is known from the oblique OB may be determined. And ©B bring addedto B=£=, found in BCi, we have =£=0,the suns distance fromthe equinoctial point =c=. Whence the time of the suns be-ing there may be fo
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