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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 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 (early Olympian gods).
Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his telescope on March 13, 1781. It had actually been seen many times before but ignored as simply another star. Herschel named it "the Georgium Sidus" (the Georgian Planet) in honor of his patron, 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.
Uranus has been visited by only one spacecraft, Voyager 2 on Jan 24 1986.
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 reason for this is unknown.
Actually, there's an ongoing battle over which of Uranus' poles is its north pole!.
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 they are made of
fairly large particles ranging from 10 meters in diameter down 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.
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.
Uranus has 15 named moons plus 2 recently discovered ones which as yet have not been given names.
Distance Radius Mass Satellite (000 km) (km) (kg) Discoverer Date --------- -------- ------ ------- ---------- ----- Cordelia 50 13 ? Voyager 2 1986 Ophelia 54 16 ? Voyager 2 1986 Bianca 59 22 ? Voyager 2 1986 Cressida 62 33 ? Voyager 2 1986 Desdemona 63 29 ? Voyager 2 1986 Juliet 64 42 ? Voyager 2 1986 Portia 66 55 ? Voyager 2 1986 Rosalind 70 27 ? Voyager 2 1986 Belinda 75 34 ? Voyager 2 1986 1986U10 75 20 ? Karkoschka 1999 Puck 86 77 ? Voyager 2 1985 Miranda 130 236 6.30e19 Kuiper 1948 Ariel 191 579 1.27e21 Lassell 1851 Umbriel 266 585 1.27e21 Lassell 1851 Titania 436 789 3.49e21 Herschel 1787 Oberon 583 761 3.03e21 Herschel 1787 Caliban 7200 30 ? Gladman 1997 Sycorax 12200 60 ? Gladman 1997
Distance Width Ring (km) (km) ------- -------- ----- 1986U2R 38000 2,500 6 41840 1-3 5 42230 2-3 4 42580 2-3 Alpha 44720 7-12 Beta 45670 7-12 Eta 47190 0-2 Gamma 47630 1-4 Delta 48290 3-9 1986U1R 50020 1-2 Epsilon 51140 20-100
(distance is from Uranus' center to the ring's inner edge)
... Sun ... Saturn
... New? ... Uranus ... Cordelia
... Neptune ...