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albedo altitude angle angular momentum appears asteroids astronomical units atmosphere attraction average axis bright brighter calculated celestial celestial sphere cent changes circle computed density determined direction disk E. E. Barnard earth earth's orbit earth's surface eccentricity elongation equal equator equatorial equinox error faint force gravity Halley's comet heavenly bodies horizon hyperbolic inclination inferior conjunction instrument interval Jupiter Jupiter's latitude less light longitude Lowell Lowell Observatory lunar lunar eclipse Mars mass mean distance measured Mercury meridian meteorites meteors miles in diameter moon motion moving nearly Neptune node object observations Observatory opposite parabolic parallax particles perihelion perturbations photograph planet planetary pole position probably radius right ascension ring rotation period satellites Saturn seen shadow sidereal period solar eclipse solar system spots star sun-spot sun's synodic period tail telescope theory tides tion transit Uranus usually velocity Venus visible Yerkes Observatory zenith
Page 266 - Thus he proposed his law of universal gravitation, which we can state as follows: Every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them.
Page 265 - Us foci (§311). (2) The radius vector of each planet describes equal areas in equal times. (3) The squares of the periods of the planets are proportional to the cubes of their mean distances from the sun ; that is, ti2 : k2 ,• ,• ai3 ,• (h3This is the so-called harmonic law.
Page 399 - Direct your telescope to a point on the ecliptic in the constellation of Aquarius, in longitude 326°, and you will find within a degree of that place a new planet, looking like a star of about the ninth magnitude, and having a perceptible disc.
Page 15 - ... is the great circle in which the plane of the earth's equator cuts the celestial sphere. It is often called the
Page 150 - There are three different kinds of year used, the sidereal, the tropical, and the anomalistic. The sidereal year is the time taken by the earth to complete one revolution around the sun from a given star to the same star again. Its length is 365 days, 6 hours, 9 minutes, and 9 seconds. The tropical year is the time included between two successive passages of the vernal equinox by the sun, and since the equinox moves westward 50.
Page 100 - Effect on the Time of Sunrise and Sunset. The horizontal refraction, ranging as it does from 34' to 39', according to temperature, is always somewhat greater than the diameter of either the sun or the moon. At the moment, therefore, when the sun's lower limb appears to be just rising, the whole disc is really below the plane of the horizon; and the time of sunrise in our latitudes is thus accelerated from two to four minutes, according to the inclination of the sun's diurnal circle to the horizon,...
Page 161 - This path turns out to be (very nearly) a great circle, inclined to the ecliptic at an angle of about 5° 8'.
Page 169 - Then again when the moon is rising we look over its upper, which is then its western edge, seeing a little more of that part of the moon than if we were observing it from the centre of the earth.
Page 161 - When the ascending node of the moon's orbit coincides with the vernal equinox, the angle between the moon's path and the celestial § 1*2] INTERVAL BETWEEN MOON'S TRANSITS. 91 equator is 23° 28...