. Astronomy for students and general readers . ectly as the linear magnitudeof the body, and inversely as its distance from the ob-server. A line seen perpendicularly subtends an angleof 1 when it is a little less than 60 times its length dis-tant from the observer (more exactly when it is 57-3lengths distant); an angle of 1 when it is 3438 lengthsdistant, and of 1 when it is 206265 lengths numbers are obtained by dividing the number ofdegrees, minutes, and seconds, respectively, in the cir-cumference, by 2 X 3 •14159265, the ratio of the circum-ference of a circle to the radius.
. Astronomy for students and general readers . ectly as the linear magnitudeof the body, and inversely as its distance from the ob-server. A line seen perpendicularly subtends an angleof 1 when it is a little less than 60 times its length dis-tant from the observer (more exactly when it is 57-3lengths distant); an angle of 1 when it is 3438 lengthsdistant, and of 1 when it is 206265 lengths numbers are obtained by dividing the number ofdegrees, minutes, and seconds, respectively, in the cir-cumference, by 2 X 3 •14159265, the ratio of the circum-ference of a circle to the radius. CIRCLES OF THE SPHERE. 5 Great Circles of the Sphere.—In Fig. 1 let the outlinerepresent that of a sphere, around which are describedthe two great circles A EB F and C E D F. These cir-cles are the lines in which two planes passing through thecentre 0 of the sphere intersect the latter. We may con-sider them as representing the planes. The points P and P, each of which is 90° distantfrom every point of the circle A E B F, are called the. Fig. 1.—SECTIONS of a spheke by planes. poles of that circle. The poles are the points in which aline passing through the centre O perpendicular to thej)lane of the circle meets the sphere. They may be con-sidered as representing this line. The angle B P, or A C, equal to the greatest distanceof the two circles, is the same as the angle which theplanes of the circles make with each other. The dis-tance between the poles P Q ov P Q is equal to the sameangle. There are therefore three equivalent representa-tives for what may be considered the same element;namely : (1) the inclination of the planes of two circles ;(2) the angle between their poles; and (3) the greatestangles, A C or B P. between the circles on the celestialsphere. ® or SYMBOLS AND ABBREVIATIONS. SIGNS OF THE PLANETS, ETC. The Earth. i Mars. n Jupiter. ^ Saturn. $ Uranus. W Neptune The asteroids are distinguished by a circle inclosing a numbe
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Keywords: ., bookcentury1800, bookdecade1880, bookpublis, booksubjectastronomy
