The Elements of Astronomy |
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Common terms and phrases
accordingly accurate actual altitude angle subtended angular diameter angular distance angular velocity annual parallax assumed astronomical axis of rotation calculated called celestial bodies celestial equator celestial meridian celestial sphere celestial vault centre circular measure clock comet corresponding declination describe determined diagram direction displacement diurnal motion earth's orbit ecliptic elongation equal equinox error evidently fact follows full moon Greenwich mean Hence horizon hour angle inclined inferior conjunction inferior planet instrument intersection interval Kepler known latitude longitude lunar disc mean noon mean sun Mercury meridian passage method moon's moreover move nearly node parallax parallel path perpendicular phase place of observation point of Aries pole precession radius refraction round the sun seen shadow sidereal day sidereal period small circle solar eclipse solstice spherical star sun's superior planet surface Suryya Siddhanta synodic period telescope tion transit Venus vertical zenith distance
Popular passages
Page 19 - All heavy things fall down to the earth by a law of nature, for it is the nature of the earth to attract and to keep things, as it is the nature of water to flow, that of the fire to burn, and that of the wind to set in motion.
Page 159 - The angle between the refracted ray and the normal to the surface at the point of refraction (qv).
Page 29 - ... stretched taut from one point to the other. The string will not lie on the parallel, but will evidently be in a plane which passes through the centre of the sphere. If the two points be on a meridian, the stretched string will lie on the meridian. By angular distance between two points on a sphere is meant the angle subtended at the centre of the sphere by the arc joining the given points. Thus in Fig. 4 the angle NOA is the angular distance of A from N.
Page 173 - D, or the distance of the body from the centre of the earth, the radius of the earth being known. Thus, since, in the case of the moon the greatest and least values of the horizontal parallax are, 61/27...
Page 12 - ... (on assumption of a stationary atmosphere) that this rotation would cause an atmospheric irregularity to affect the red rays first and the violet last, violet first and red last, and all rays more or less simultaneously, of stars in the west, east, and near the meridian, respectively. But the order would be the same if the earth were at rest and the air travelling from west to east.
Page 59 - Right ascension is either estimated in degrees, minutes, &c. from 0° to 1560° ; or in hours, minutes, &c. of time, 15 degrees being allowed for each hour, as in Sph. Trig. § 3. The positions of the stars are completely determined upon...
Page 124 - These are: (1) The orbits of the planets are ellipses, with the sun at a common focus. (2) As a planet moves in its orbit, the line joining the planet and sun sweeps over equal areas in equal intervals of time. Also called "law of equal areas.
Page 12 - And the fact that the motions of the sun, the moon and the planets are all confined to a narrow belt with the ecliptic...
Page 8 - Krttika (the Pleiades) as the sign of the vernal equinox. But this arrangement would be correct only about 2300 BC and nowhere else would be found a well-authenticated Zodiacal sequence of so early a date. If this be granted, it seems to be very probable that the method of signs was...