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    PHYSICAL URANUS


    Uranus is the seventh planet from the Sun and the third largest (by diameter). Uranus is larger in diameter but smaller in mass than Neptune.

    
    orbit:    2,870,990,000 km (19.218 AU) from Sun
    diameter: 51,118 km (equatorial)
    mass:     8.683e25 kg 

    Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematicly searching the sky with his telescope on March 13, 1781. It had actually been seen many times before but ignored as simply another star (the earliest recorded sighting was in 1690 when John Flamsteed cataloged it as 34 Tauri). Herschel named it "the Georgium Sidus" (the Georgian Planet) in honor of his patron, the infamous (to Americans) King George III of England; others called it "Herschel". The name "Uranus" was first proposed by Bode in conformity with the other planetary names from classical mythology but didn't come into common use until 1850.

    Most of the planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus' axis is almost parallel to the ecliptic. At the time of Voyager 2's passage, Uranus' south pole was pointed almost directly at the Sun. This results in the odd fact that Uranus' polar regions receive more energy input from the Sun than do its equatorial regions. Uranus is nevertheless hotter at its equator than at its poles. The mechanism underlying this is unknown.

    Actually, there's an ongoing battle over which of Uranus' poles is its north pole! Either its axial inclination is a bit over 90 degrees and its rotation is direct, or it's a bit less than 90 degrees and the rotation is retrograde. The problem is that you need to draw a dividing line *somewhere*, because in a case like Venus there is little dispute that the rotation is indeed retrograde (not a direct rotation with an inclination of nearly 180).

    Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium (in contrast to Jupiter and Saturn which are mostly hydrogen). Uranus (and Neptune) are in many ways similar to the cores of Jupiter and Saturn minus the massive liquid metallic hydrogen envelope. It appears that Uranus does not have a rocky core like Jupiter and Saturn but rather that its material is more or less uniformly distributed.

    Uranus' atmosphere is about 83% hydrogen, 15% helium and 2% methane.

    Like the other gas planets, Uranus has bands of clouds that blow around rapidly. But they are extremely faint, visible only with radical image enhancement of the Voyager 2 pictures (right). Recent observations with HST (left) show larger and more pronounced streaks. Further HST observations show even more activity. Uranus is no longer the bland boring planet that Voyager saw! It now seems clear that the differences are due to seasonal effects since the Sun is now at a lower Uranian latitude which may cause more pronounced day/night weather effects. By 2007 the Sun will be directly over Uranus's equator.

    Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere. There may be colored bands like Jupiter's but they are hidden from view by the overlaying methane layer.

    Like the other gas planets, Uranus has rings. Like Jupiter's, they are very dark but like Saturn's composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 11 known rings, all very faint; the brightest is known as the Epsilon ring. The Uranian rings were the first after Saturn's to be discovered. This was of considerable importance since we now know that rings are a common feature of planets, not a peculiarity of Saturn alone.

    Voyager 2 discovered 10 small moons in addition to the 5 large ones already known. It is likely that there are several more tiny satellites within the rings.

    Uranus' magnetic field is odd in that it is not centered on the center of the planet and is tilted almost 60 degrees with respect to the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus.

    Uranus is sometimes just barely visible with the naked eye on a very clear night; it is fairly easy to spot with binoculars (if you know exactly where to look). A small astronomical telescope will show a small disk. Mike Harvey's planet finder charts show the current position of Uranus (and the other planets) in the sky, but much more detailed charts will be required to actually find it. Such charts can be created with a planetarium program such as Starry Night.

    Uranus has 15 named moons plus 2 recently discovered ones which as yet have not been given names.

    Unlike the other bodies in the solar system which have names from classical mythology, Uranus' moons take their names from the writings of Shakespeare and Pope. They form two distinct classes: the 10 small very dark inner ones discovered by Voyager 2 and the 5 large outer ones (right). They all have nearly circular orbits in the plane of Uranus' equator (and hence at a large angle to the plane of the ecliptic).

    SATELLITES

    Cordelia
    Ophelia
    Bianca
    Cressida
    Desdemona
    Juliet
    Portia
    Rosalind
    Belinda
    Puck
    Miranda
    Ariel
    Umbriel
    Titania
    Oberon
    Caliban
    Sycorax



    MYTHOLOGY



    Uranus is the sky god and first ruler. He is the son of Gaea, who created him without help. He then became the husband of Gaea and together they had many offspring, including twelve of the Titans.

    Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus was the son and mate of Gaia the father of Cronus (Saturn) and of the Cyclopes and Titans (predecessors of the Olympian gods).

    Cronus was the ruling Titan who came to power by castrating his Father Uranus. His wife was Rhea. There offspring were the first of the Olympians. To insure his safety Cronus ate each of the children as they were born. This worked until Rhea, unhappy at the loss of her children, tricked Cronus into swallowing a rock, instead of Zeus. When he grew up Zeus would revolt against Cronus and the other Titans, defeat them, and banish them to Tartarus in the underworld.

    Cronus managed to escape to Italy, where he ruled as Saturn. The period of his rule was said to be a golden age on earth, honored by the Saturnalia feast.



    METAPHYSICS



    ASTROLOGY

    Uranus rules Aquarius - the planet for sudden change.

    Uranus: Breakthroughs and Revolution.

    Uranus, discovered between the American and French revolutions, symbolizes our capacity to go beyond limits. It is about inventiveness, originality and independence. "Uranian" people (those marked strongly by this planet) are unique individuals who act as agents for change, they are awakeners here to help us break our patterns.

    Astrology link

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