Recreations in Astronomy Part 21

JUPITER, apparent path of, in 1866, 112; elements of, 164; satellites of, 165; positions of satellites, 166; elements of satellites, 166; the Jovian system, 167.

KEPLER'S LAWS--1st, that the orbits of planets are ellipses, having the sun or central body in one of the foci; 2d, the radius-vector pa.s.ses over equal s.p.a.ces in equal times; 3d, the squares of the periodic times of the planets are in proportion to the cubes of their mean distances from the sun.

LAt.i.tUDE, the angular distance of a heavenly body from the ecliptic.

LIGHT, the child of force, 17; number of vibrations of, 18, 25; velocity of, 22; undulatory and musical, 26; chemical force of, 30; experiments with, 37; approach and departure of a light-giving body measured, 51; aberration of, 199.

LIMB, the edge of the disk of the moon, sun, or a planet.

LONGITUDE. If a perpendicular be dropped from a body to the ecliptic, its celestial longitude is the distance of the foot of the perpendicular from the vertical equinox, counted toward the east; mode of ascertaining terrestrial, 72.

MAGELLANIC CLOUDS, 208.

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MARS, 159; snow spots of, 160; satellites of, 161.

Ma.s.s, the quant.i.ty of matter a body contains.

MEAN DISTANCE OF A PLANET, half the sum of the aphelion and perihelion distances.

MEASUREMENTS, celestial, 57.

MERCURY, 138.

MERIDIAN, terrestrial, of a place, a great circle of the heavens pa.s.sing through the poles, the zenith, and the north and south points of the horizon; celestial, any great circle pa.s.sing from one pole to the other.

METEORS, 119; swarm of, meeting the earth, 118; explosion of, 120; systems of, 123; relation of, to comets, 124.

MICROMETER, any instrument for the accurate measurement of very small distances or angles.

MIND, origin of force, 252; continuous relation of, to the universe, 252.

MILKY WAY, 210, 215.

MIRA, the Wonderful, 221.

MOON, the, 151; greatest and least distance from the earth, 10; telescopic appearance of, 155.

MURAL CIRCLE, 61.

NADIR, the point in the celestial sphere directly beneath our feet, opposite to zenith.

NEBULae, 217.

NEBULAR HYPOTHESIS, not atheistic, 182; stated, 182; confirmatory facts, 183; objections to, 185.

NEPTUNE, elements of, 175.

NODE, the point in which an orbit intersects the ecliptic, or other plane of reference; ascending, descending, line of, 107.

OCCULTATION, the hiding of a star, planet, or satellite by the interposition of a nearer body of greater angular magnitude.

OPPOSITION. A superior planet is in opposition when the sun, earth, and the planet are in a line, the earth being in the middle.

ORBIT, the path of a planet, comet, or meteor around the sun, or of a satellite around a primary; inclination of, 106; earth's, seen from the stars, 70.

OUTLINE FOR STUDENTS, 276.

PARALLAX, the difference of direction of a heavenly body as seen from two points, as the centre of the earth and some point of its surface, 69.

PARALLELS, imaginary circles on the earth or in the heavens parallel to the equator, having the poles for their centre.

PERIGEE, nearest the earth; said of a point in an orbit.

PERIHELION, the point of an orbit nearest the sun.

PERIODIC TIME, time of a planet's, comet's, or satellite's revolution.

PERSONAL EQUATION, 65.

PERTURBATION, the effect of the attractions of the planets or other [Page 283]

bodies upon each other, disturbing their regular motion; of Saturn and Jupiter, 11; of asteroids, 13; of Ura.n.u.s and Neptune, 176.

PHASES, the portions of the illuminated half of the moon or interior planet, as seen from the earth, called crescent, full, and gibbous.

PHOTOSPHERE of the sun, 89.

PLANET (_a wanderer_), as seen from s.p.a.ce, 99; speed of, 101; size of, 102; movements retrograde and direct, 112.

POINTERS, the, 197.

POLE, NORTH, movement of, 198.

POLES, the extremities of an imaginary line on which a celestial body rotates.

QUADRANT, the fourth part of the circ.u.mference of a circle, or 90.

QUADRATURE, a position of the moon or other body when 90 from the sun.

RADIANT POINT, that point of the heavens from which meteors seem to diverge, 118.

RADIUS-VECTOR, an imaginary line joining the sun and a planet or comet in any part of its...o...b..t.

RAIN, weight of, 249.

REFLECTING TELESCOPE, 44.

REFRACTING TELESCOPE, 43.

REFRACTION, a bending of light by pa.s.sing through any medium, as air, water, prism.

RETROGRADE MOTION, the apparent movement of a planet from east to west among the stars.

REVOLUTION, the movement of bodies about their centre of gravity.

ROTATION, the motion of a body around its axis.

SATELLITES, smaller bodies revolving around planets and stars.

SATURN, elements of, 167; revolution of, 168; rings of, 169; decreasing, 171; nature of, 171; satellites of, 172.

SEASONS, of the earth, 102; of other planets, 105.

SELENOGRAPHY (_lunography_), a description of the moon's surface.

SIGNS OF THE ZODIAC, the twelve equal parts, of 30 each, into which the zodiac is divided.

SOLAR SYSTEM, view of, 100, 177.

SOLSTICES, those points of the ecliptic which are most distant from the equator. The sun pa.s.ses one about June 21st, and the other about December 21st, giving the longest days and nights.

SPECTROSCOPE, 46.

SPECTRUM OF SUN AND METALS, 50.

STARS, chemistry of, 28; distance of, 70-73; mode of naming, 196; number of, 210; double and multiple, 210; colored, 214; cl.u.s.ters of, 215; variable, 220; temporary, new, and lost, 223; movements of lateral, 226; in line of sight, 269.

STATIONARY POINTS, places in a planet's...o...b..t at which it has no motion among the stars.

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STELLAR SYSTEM, the, 195.

SUMMARY OF RECENT DISCOVERIES, 269.

SUN, fall of two meteoric bodies into, 19; light from contraction of, 20; as seen from planets, 79; corona, 81; hydrogen flames of, 84; condition of, 89; spots, 90; experiments, 95; apparent path among the stars, 111; power of, 250.

SYMBOLS USED IN ASTRONOMY, 275.

TELESCOPE, refracting, 43; reflecting, 44; Cambridge equatorial, 46.

TELESCOPIC WORK, cl.u.s.ters, 210; double stars, 212.

TEMPORARY STARS, 223.

TERMINATOR, the boundary-line between light and darkness on the moon or a planet.

TIDES, 146.

TRANSIT, the pa.s.sage of an object across some fixed line, as the meridian, or between the eye of an observer and an apparently larger object, as that of Mercury or Venus over the disk of the sun, and the satellites of Jupiter over its disk; of a star, 65.

ULTIMATE FORCE, the, 249.

URa.n.u.s, elements of, 173; moons of, retrograde, 174; perturbed by Neptune, 176.

VARIABLE STARS, 220.

VENUS, 139.

VERNIER, a scale to measure very minute distances.

VERTICAL CIRCLE, one that pa.s.ses through the zenith and nadir of the celestial sphere. The prime vertical circle pa.s.ses through the east and west points of the horizon.

VULCAN, discovery of, 137.

WORLDS, THE, AND THE WORD, teach the same truth, 231-245.

YEAR, the, length of, on any planet, is determined by the periodic time.

ZENITH, the point in the celestial sphere directly overhead.

ZODIAC, a belt 18 wide encircling the heavens, the ecliptic being the middle. In this belt the larger planets always appear. In the older astronomy it was divided into twelve parts of 30 each, called signs of the zodiac.

ZODIACAL LIGHT, 80.

TO FIND THE STARS IN THE SKY.

Detach any of the following maps, appropriate to the time of year, hold it between you and a lantern out-of-doors, and you have an exact miniature of the sky. Or, better, cut squares of suitable sizes from the four sides of a box; put a map over each aperture; provide for ventilation, and turn the box over a lamp or candle out-of-doors. Use an opera gla.s.s to find the smaller stars, if one is accessible.

[Ill.u.s.tration: Circ.u.mpolar Constellations. Always visible. In this position.--January 20th, at 10 o'clock; February 4th, at 9 o'clock; and February 19th, at 8 o'clock.]

[Ill.u.s.tration: Algol is on the Meridian, 51 South of Pole.--At 10 o'clock, December 7th; 9 o'clock, December 22d; 8 o'clock, January 5th.]