Astronomy in a nutshell, the chief facts and principles explained in popular language for the general reader and for schools . , XIV, XV, XVI, XVII,XVIII, XIX, XX, XXI, XXII, XXIII, xxiv— are employed for the hours, and the lettersm and s respectively for the minutes andseconds. Since there are 3600 in everycircle, it is plain that one hour of right ascen-sion corresponds to 150. So, too, one minuteof right ascension corresponds to 15, andone second to 15. It will be found usefulto memorise these relations. 7. Effects Produced by Changing theObservers Place on the Earth. The readerwill recall
Astronomy in a nutshell, the chief facts and principles explained in popular language for the general reader and for schools . , XIV, XV, XVI, XVII,XVIII, XIX, XX, XXI, XXII, XXIII, xxiv— are employed for the hours, and the lettersm and s respectively for the minutes andseconds. Since there are 3600 in everycircle, it is plain that one hour of right ascen-sion corresponds to 150. So, too, one minuteof right ascension corresponds to 15, andone second to 15. It will be found usefulto memorise these relations. 7. Effects Produced by Changing theObservers Place on the Earth. The readerwill recall that in Sect. 4 we described an-other system of circles for determining theplaces of stars, a system based on the horizonand the zenith. This horizon-zenith systemtakes no account of the changes producedby the apparent motion of the heavens,and consequently it is not applicable todetermining the absolute positions of thestars on the celestial sphere. It simplyshows their positions in the visible half ofthe sky, as seen at some particular timefrom some definite point on the earth. In After Shifting Observers Position 35. Fig. 3. Right Ascension and Declination. The plane of the horizon, with the north, south, east, and west points, and the zenith, are represented as in Fig. 2. P and P are the poles of the celestial sphere, the dotted line connecting them representing the direction of the axis, both of celestial sphere and the earth. The circle Eq Eq is the equator. V is the vernal equinox, or the point on the equator whence right ascension is reckoned round toward the east. The circle passing through s, parallel to the equator, is a declination circle. The circle P s P is the hour circle of the star s. The arc of this hour circle contained between s and the point where it meets the equator is the stars declination. Its right ascension is measured by the arc of the equator contained between V and the point where its hour circle meets the equator, or by the angle V P s. The hour
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Keywords: ., bookcentury1900, bookdecade19, booksubjectastronomy, bookyear1912
