ASTRONOMY

1. URANUS. 2. MERCURY. 3. VENUS. 4. THE MDON. 5. THE EARTH (SUMMER SOLSTICE). 6 THE SUN (SHOWING SPOTS AND PROMINENCES). 7. MARS. 8 SATURN. 9. JUPITER, 1D 264 265 Nautical of on the cu es and of The travelling same planet the own fixed axis prece ion The (q.v.), mark able be between is earth’s eclipse. is The in from mean together its term in est he sun are act suns tremendous the telescopes. into venience cla ification. to revolving shot, keeping some composed sembling telescopes dividual the sider able recorded and took calculate Chaldean by the round eccentricity solar ( 237) Astronomy. astronomy is an application to the needs navigators for the determination of position the earth by means of the configurations in celestial sphere. Physical astronomy disthe forces which cause motion, the analysis composition, early history, and development the heavenly bodies. [SPECTRUM ANALYSIS. ] sun is the centre of a system of planets round it, all of them very nearly in the plane. One of these is our earth. Each has its year, or period of revolution round sun, and its day, or period of rotation about its axis. The axis of a planet does not remain in direction, but “ wobbles” slowly, like the of a spinning top. This wobbling is called (q.v.). Some of these planets have satellites of their own. earth's satellite is the moon (q.v). Saturn besides having ten moons, has a very rering round it—the nature of which will discu ed separately. When the moon intervenes the earth and the sun, part of the latter obscured, and we have a solar eclipse. If the shadow falls on the moon we have a lunar When the space between earth and sun traversed by another planet we have a transit. transits of Venus are of very great importance the accurate estimation of the sun’s distance the earth—about 92,000,000 miles being its value. The variation of the sun's distance, with the obliquity of the earth’s axis to ecliptic or plane of motion round the sun, deseasons. The attraction of the moon and on the waters of the earth produce tides, which of greater or le extent as the sun and moon in conjunction or oppose each other’s effects. Besides our sun, there are innumerable other in the universe, i.e. the stars, but at such distances that they are but points in heavens even when viewed with the largest The stars were fancifully arranged constellations by the ancients, and for con the old names are still employed in Hundreds of stars have been found be double, i.e. they exist in pairs, each pair about the common ma -centre, like chain but with only the immaterial link of gravity them together. Finally, we have nebule, consisting of matter in a gaseous state, others of immense aggregations of stars refaintly luminous clouds, and requiring of high power to resolve them into instars. The Milky Way is an example of latter. Astronomy was studied by the ancients to a con extent. The Chinese are said to have a conjunction of Saturn, Jupiter, Mars, Mercury with the moon, which phenomenon place B.c. 2500. The Indians were able to eclipses, and certain observations of the astronomers have been proved to be true recent calculations. Aristarchus (260 B.c.) taught double motion of the earth round the sun and its own axis. Hipparch us determined the of the earth’s orbit, the length of the year, noted the prece ion of the equinoxes, and system century; the and Copernicus that Kepler, Tycho motion of that advance development covery out plates, lacral is of ing flexible interambulacral able Sea-urchins. FERA, sand, Astrarhizide, Biblical was was book principally in goshawk the Rome. believed was the the now along the east 4,091 the takes up highest The grapes, abundant. valued. the Asturias. started a catalogue of stars The Ptolemaic (q.v.) was propounded in the second it regarded the earth as the centro of universe, round which revolved the sun, mcon, planets. It held sway till the time of in the sixteenth century, who taught the sun was the centre of our system. Then chiefly by means of the observations of Brahe, arrived at his three laws of planetary (q.v.). Newton gave the world his theory gravitation and the laws of motion, and from time to the present, chiefly on account of the in optical science and the consequent of the telescope, astronomical dis. has progre ed to an amazing extent. Astropectenidsa, 1 family of STARFISH with an us, but with pointed tube feet, large marginal and internal plates supporting the ambuplates. The type genus is Astropecten, which first found in the jura ic rocks. Ca ell's Encyclopedia of General Information Vol. 1