475. Vesta is the only asteroid that can be seen with the naked eye. 476. The largest of the asteroids is probably about 220 mile diameter; the smallest is less than 20 miles. 477. The following table comprises their names, &c.: TABLE OF THE ASTEROIDS. 4. Vesta.... ..... Olbers 1. Ceres... 2. Pallas. 252,959,381 1,681 March 28, 1802 Olbers.. Palermo. 3. Junc.. Harding. Lilienthal. Bremen. 5. Astra.. 1845 Hencke.. Dresden. 6. Hebe. 1847 Hencke.. Dresden. 243.971.812 1,592 Sept. 1, 1804 215,893.6591,325 March 29, 1807 235,631,270 1,511 Dec. 8, 221,797,635 1.380 July 1, 218,173,325 1,346 Aug. 13, 201.273.1271,193 Oct. 18, 218.211.451 1,347 April 25, 288,110,375 2.043 April 12, 11. Parthenope.. 224,181,315 1,402 May 13, 213,597.600 1.302 Sept. 13, 235,581,675 1,511 Nov. 2, 236,441,215 1,519 May 20, 241,712,109 1,570 July 29, 267,311,899 1,826 March 17, 226,156,795 1,421 April 17, 209,891,225 1,270 June 24, 223,195,117 1,393 Aug. 22, 220,311,715 1,366 Sept. 19, 222,673,235 1,388 Nov. 15, 265,988,156 1,814 Nov. 16, 240,194,177 1,555 Dec. 15, 287,371,205 2,035 April 5, 219,507,125 1,359 April 6, 1851 De Gasparis. Naples. Bilk. 27. Euterpe.. 28. Bellona.. 214,561,317 1,313 Nov. 8, 66 Hind London. 1854 " 216,275,879 1,329 July 22, 66 66 66 Goldschmidt. Paris. 66 Chacornac.. Paris. 1855 Chacornac.. Paris. 66 Luther.. Bilk. 65. Cybele.. 66. Maia... 67. Asia.... 68. Leto... Goldschmidt. Paris. Searle... Albany, N. 7, Bilk Chacornac.. Paris. Ferguson.. Washington, D.O Foster..... Berlin. De Casparis Tempel... Naples. Marseilles. Cambridge, Masa 66 66 1861 Tempel. 66 Tuttle Bilk. 64. Angelina... 245.117,875 1,603 March 2, 9. Eurynome..| 223,379,507 1,395 Sept. 14, Marseilles. Clinton, N. Y. Copenhagen. Clinton, N. Y. Bilk. Ann Arbor, Mich Marseilles. Bilk. Clinton, N. Y. Berlin. Madras. 1865 De Gasparis. Naples. Luther... Bilk. Peters.. 66 246,638.250 1,616 Oct. 9, Clinton, N. Y Marseilles. Clinton, N. Y. Ann Arbor, Mich. Marseilles. Ann Arbor, Mich Ann Arbor, Mich Bilk. Birce the discovery of Felicitas, nineteen other asteroids have been announco making the whole Lumber, up to 1873, one hundred and twenty-eight. CHAPTER VII. PRIMARY PLANETS-JUPITER ANƆ SATURN. 473. JUPITER is the largest of all the planets belonging to the volar system. It may be readily distinguished from the fixed tars, by its peculiar splendor and magnitude; appearing to the aaked eye almost as resplendent as Venus, although it is more han seren times her distance from the Sun. When his right ascension is less than that of the Sun, he is our morning star, and appears in the eastern hemisphere before the Sun rises; when greater, he is our evening star, and lingers in the western hemisphere after the Sun sets. Nothing can be easier than to trace Jupiter among the con stellations of the zodiac; for in whatever constellation he is seen to-day, one year hence he will be seen equally advanced in the next constellation; two years hence, in the next; three years hence, in the next, and so on; being just a year, at a mean rate in passing over one constellation. The exact mean motion of Jupiter in its orbit, is about one-twelfth of a degree in a day which amounts to only 30° 20' 32" in a year. For 12 years to come, he will, at a mean rate, pass through the constellations of the zodiac, as follows: 479. Jupiter is the next planet in the solar system above th asteroids, and performs his annual revolution around the Sun in nearly 12 of our years, at the mean distance of 475,000,000 of miles; moving in his orbit at the rate of 29,000 miles an hour. The exact period of Jupiter's sidereal revolution is 11 years, 10 months, 17 days, 14 hours, 21 minutes, 25 seconds. Ilis exact mean distance from the Sun is 475.693,000 miles; consequently, the exact rate of his motion in his orbit is 28,744 miles per hour 480. He revolves on an axis, which is nearly perpendicular to the plane of his orbit, in 9 hours, 55 minutes, and 50 seconds; 30 that his year contains 10,471 days and nights; each about 5 hours long. His form is that of an oblate spheroid, whose polar diameter 478. Comparative size of Jupiter? How distinguished from the fixed stars? When Borning star, &c.? Is he easily traced! 479. His position in the system? His peri ale time? Distance from the Sun? Rate of motion? 480. Time of diurna. revcia Hoa! Position of axis? Length of his days? Number in his year? His form Catial 11 bis oblateness? Difference of equatorial and polar diameters? The Earth? is to its equatorial, as 16 to 17. He is therefore considerably more flattened at the poles than any of the other planets, except Saturn. This is caused by his rapid rotation on his axis; for it is an universal law that the equatorial parts of every body, revolving on an axis, will be swollen out, in proportion to the tensity of the body and the rapidity of its motion. The difference between the polar and equatorial diameters of Jupiter, excee is 5000 niles. The difference between the polar and equatorial diameters of the Earth, is only miles. Jupiter, even on the most careless view through a good telescope, appears to be oval; the longer diameter being parallel to the direction of his belts, which are also parallel to the ecliptic. 481. By this rapid whirl on its axis, his equatorial inhabitants are carried around at the rate of 27,600 miles an hour; which is 2700 miles farther than the equatorial inhabitants of the Earth are carried, by its diurnal motion, in twenty-four hours. The true mean diameter of Jupiter is 85,390 miles; which is nearly 11 times greater than the Earth's. His volume is, therefore, about thirteen hundred times larger than that of the Earth. (For magnitude as compared with that of the Earth, se Map I.) On account of his great distance from the Sun, the degree of light and heat which he receives from it is 27 times less than that received by the Earth. When Jupiter is in conjunction, he rises, sets, and comes to the meridian with the Sun' out is never observed to make a transit, or pass over the Sun's disc; when in opposition. be rises when the Sun sets, sets when the Sun rises, and comes to the meridian at mid aight, which never happens in the case of an interior planet. This proves that Jupiter revolves in an orbit which is exterior to that of the Earth. 482. As the variety in the seasons of a planet, and in the length of its days and nights, depends upon the inclination of its axis to the plane of its orbit, and as the axis of Jupiter ha little or no inclination, there can be no difference in his seasons. on the same parallels of latitude, nor any variation in the lengt of his days and nights. It is not to be understood, however that one uniform season prevails from his equator to his poles but that the same paraliels of latitude on each side of his equa tor, uniformly enjoy the same season, whatever season it may be. About his equatorial regions there is perpetual summer; and at his poles everlasting winter; but yet equal day and equal! night at each. This arrangement seems to have been kindly ordered by the beneficent Creator; for had his axis been inclined o his orbit, like that of the Earth, his polar winters would have een alternately a dreadful night of six years' darkness. 41. Motion at Jupiter's equator? His mean diameter? His volume? Light and heat Does he ever transit the Sun? What proof that his orbit is exterior to that of the Earth! 2. What of the seasons of Jupiter? What apparent manifestation of Divine Wisdom, 483 Jupiter, when viewed through a telescope, appears to be surrounded by a number of luminous zones, usually termed beits, that frequently extend quite around him. These belts are parallel not only to each other, but, in general, to his equator, which is also nearly parallel to the ecliptic. They are subject, however, to considerable variation, both in breath and aumber. Sometimes eight have been seen at once; sometimes only one, but more usually three. Dr. Herschel once perceived his whole disc covered with small belts, though they are more usually confined to within 30° of his equator, that is, to a zone 60° in width. Sometimes these belts continue for months at a time with little or no variation, and sometimes a new belt has been seen to form in a few hours. Sometimes they are interrupted in their length; and at other times, they appear to spread in width, and run into each other, until their breadth exceeds 5000 miles. 484. Bright and dark spots are also frequently to be seen in the belts, which usually disappear with the belts themselves, though not always, for Cassini observed that one occupied the same position more than 40 years. Of the cause of these variable appearances, but little is known. They are generally supposed to be nothing more than atmospherical phenomena, resulting from, or combined with, the rapid motion of the planet upon its axis. Different opinions have been entertained by astronomers respecting the cause of these belts and spots. By some they have been regarded as clouds, or as openings in the atmosphere of the planet, while others imagine that they are of a more permanent nature, and are the marks of great physical revolutions, which are perpetually agitating and changing the surface of the planet. The first of these opinions sufficiently explain the variations in the form and magnitude of the spots, and the parallelism of the te 483. How does Jupiter appear through a telescope? Where are his belts usually seen? Their number? Are they permanent? 454. What else seen upon Jupiter's surface? Are they permanent? Is the cause of these phenomena well understord' What different opinions? |