Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

URANUS

Online Encyclopedia
Originally appearing in Volume V27, Page 789 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

URANUS , in See also:

astronomy, the seventh See also:major See also:planet in the See also:order of distance from the See also:sun, and denoted by the See also:symbol a or W. It was discovered by the See also:elder See also:Herschel on the 13th of See also:March 1781. He saw it as a See also:round nebulous disk, slowly moving among the stars, and at first supposed it to be a See also:comet, and announced it as such to the Royal Society. But a few See also:weeks' observation showed it to be moving in a nearly circular See also:orbit at a distance from the sun about nineteen times that of the See also:earth. Its planetary See also:character was thus established, and Herschel named it the Georgium Sidus in See also:honour of his royal See also:patron. This name was See also:long recognized in See also:England, and " the Georgian " was officially used in the Nautical See also:Almanac up to 185o. But it was never received with favour on the See also:continent of See also:Europe, nor was that of the discoverer, which was proposed by See also:Lalande. The name Uranus was proposed by See also:Bode, and adopted everywhere outside of England. As seen in a See also:telescope of the highest See also:power, Uranus presents to the See also:eye the See also:appearance of a disk about four seconds in See also:diameter of a faint See also:sea-See also:green tint. No trace of a marking can be seen on the See also:surface, and, so far as See also:measures have yet been made on it, no deviation of the disk from a circular See also:form has been established. Nothing is therefore known as to its axial rotation. Although the planet is commonly considered a telescopic one, it is really of the See also:sixth magnitude, and therefore faintly visible to the naked eye if one knows precisely where to look for it.

Long before its See also:

discovery it had been observed as a fixed See also:star by J. See also:Flamsteed. P. C. See also:Lemonnier also made eight observations of it during the opposition of 1768-69, which would have revealed its planetary character had he reduced and compared them. For other particulars See also:relating to Uranus, its spectrum, &c., see PLANET. Satellites of Uranus.—In See also:January 1787 Herschel detected two satellites of Uranus of which the inner one, now known as Titania, had a See also:period of 9 days, the See also:outer, See also:Oberon, of 13z days. He also on other occasions saw what he supposed to be two additional satellites, but careful investigation of his observations has shown that the supposed See also:objects could not have been of this character. But in 1851–52 See also:William Lassell at See also:Malta, in See also:conjunction with his assistant A. Marth, observed two satellites yet nearer the planet than those of Herschel. These are now known as Ariel and Umbriel. Their periodic times are about 2-1 and 4 days respectively.

Lassell's telescopes, which were reflectors, were See also:

superior to others of his See also:time in See also:light-power, and these inner satellites were not seen by other astronomers for more than twenty years after their discovery. Indeed, doubts of their reality sometimes found expression until, in 1873, they were observed with the See also:Washington 26-See also:inch telescope, and observations upon them showed their identity with the objects discovered by Lassell. The greater difficulty in seeing the inner than the outer satellites arises from their proximity to the planet. There is no very See also:great difference in the actual brightness of the four objects. It is found that Umbriel, though less easy to see than Titania, actually exceeds it in light. But none of them has been seen except in a few of the most powerful telescopes. The most remarkable feature of these bodies is that, instead of the planes of their orbits being near that of the See also:ecliptic, they are actually inclined to it nearly 900. The result is that, as the planet performs its orbital revolution, there are two opposite points near which the orbits are seen edgewise, and the satellites seem to us to See also:swing See also:north and See also:south on each See also:side of the planet. This was the See also:case in 1882, and will be the case again in 1924. At the points midway between these two, through which the planet passed in 1861 and 1903, and will pass again in 1945, the orbits are seen almost perpendicularly, so that the apparent orbit, like the real one, is nearly circular. Orbits of the Satellites of Uranus.—So far as has yet been determined, the four satellites all revolve in the same See also:plane, the position of which, referred to the Earth's See also:equator and See also:equinox, is R.A. of ascending See also:node, 166°•o5+o°•o142ot. Inclination of orbit, 75°•28-0°•00131.

None of the orbits seems to have a measurable eccentricity. The positions of the satellites in the orbits at any time may be found from the following elements, where u is the angular distance from the node upon a plane parallel to that of the Earth's equator, and the See also:

motion is that in a See also:Julian See also:year. See also:Satellite. u at See also:Annual Motion. Daily Mean A Epoc h . Motion. Dist. Ariel 22°•61 579 rev. +242°•64 142°•836 13"•78 Umbriel 136°•49 352 ,, +195°'31 86°'869 19".20 Titania 229°'93 167 „ +294°'20 41°•351 31"<48 Oberon 154°.90 1o8 „ +186°.27 26°•739 42"•10 The See also:epoch force is 1872, January o, Washington mean See also:noon. The mean distance is the See also:angle subtended by the See also:radius of the orbit as seen at the mean distance of Uranus from the Sun (See also:log a=1.28310).

End of Article: URANUS

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
URANIUM [symbol U, atomic weight 238.5 (0=16)] 		[next]
URANUS (Heaven)

Site © 2006 - Net Industries