ranus has 21 named moons and six unnamed ones: 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 three distinct classes: the 11 small very dark inner ones discovered by Voyager 2, the 5 large ones (right), and the newly discovered much more distant ones. Most have nearly circular orbits in the plane of Uranus' equator (and hence at a large angle to the plane of the ecliptic); the outer 4 are much more elliptical.

	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
2003U2	75	6	?	Showalter	2003
Belinda	75	34	?	Voyager 2	1986
1986U10	76	40	?	Voyager 2	1986
Puck	86	77	?	Voyager 2	1985
2003U1	98	8	?	Showalter	2003
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
2001U3	4281	6	?	Sheppard	2003
Caliban	7169	40	?	Gladman	1997
Stephano	7948	15	?	Gladman	1999
Trinculo	8578	5
Sycorax	12213	80	?	Nicholson	1997
2003U3	14689	6	?	Sheppard	2003
Prospero	16568	20	?	Holman	1999
Setebos	17681	20	?	Kavelaars	1999
2002U2	21000	6		2003	2003

Uranus' Rings

	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)
Neptune is the eighth planet from the Sun and the fourth largest (by diameter). Neptune is smaller in diameter but larger in mass than Uranus.
orbit:4,504,000,000 km (30.06 AU) from Sun
diameter:49,532 km (equatorial)
mass: 1.0247e26 kg

In Roman mythology Neptune (Greek: Poseidon) was the god of the Sea
After the discovery of Uranus, it was noticed that its orbit was not as it should be in accordance with Newton's laws. It was therefore predicted that another more distant planet must be perturbing Uranus' orbit. Neptune was first observed by Galle and d'Arrest on 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus. An international dispute arose between the English and French (though not, apparently between Adams and Le Verrier personally) over priority and the right to name the new planet; they are now jointly credited with Neptune's discovery. Subsequent observations have shown that the orbits calculated by Adams and Le Verrier diverge from Neptune's actual orbit fairly quickly. Had the search for the planet taken place a few years earlier or later it would not have been found anywhere near the predicted location.

More than two centuries earlier, in 1613, Galileo observed Neptune when it happened to be very near Jupiter, but he thought it was just a star. On two successive nights he actually noticed that it moved slightly with respect to another nearby star. But on the subsequent nights it was out of his field of view. Had he seen it on the previous few nights Neptune's motion would have been obvious to him. But, alas, cloudy skies prevented obsevations on those few critical days

Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. Much of we know about Neptune comes from this single encounter. But fortunately, recent ground-based and HST observations have added a great deal, too.

Because Pluto's orbit is so eccentric, it sometimes crosses the orbit of Neptune making Neptune the most distant planet from the Sun for a few years.

Neptune's composition is probably similar to Uranus': various "ices" and rock with about 15% hydrogen and a little helium. Like Uranus, but unlike Jupiter and Saturn, it may not have a distinct internal layering but rather to be more or less uniform in composition. But there is most likely a small core (about the mass of the Earth) of rocky material. Its atmosphere is mostly hydrogen and helium with a small amount of methane.

Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere but there is some additional as-yet-unidentified chromophore which gives the clouds their rich blue tint.

Like a typical gas planet, Neptune has rapid winds confined to bands of latitude and large storms or vortices. Neptune's winds are the fastest in the solar system, reaching 2000 km/hour.

Like Jupiter and Saturn, Neptune has an internal heat source -- it radiates more than twice as much energy as it receives from the Sun.
At the time of the Voyager encounter, Neptune's most prominent feature was the Great Dark Spot in the southern hemisphere. It was about half the size as Jupiter's Great Red Spot (about the same diameter as Earth). Neptune's winds blew the Great Dark Spot westward at 300 meters/second (700 mph). Voyager 2 also saw a smaller dark spot in the southern hemisphere and a small irregular white cloud that zips around Neptune every 16 hours or so now known as "The Scooter". It may be a plume rising from lower in the atmosphere but its true nature remains a mystery.
However, HST observations of Neptune (left) in 1994 show that the Great Dark Spot has disappeared! It has either simply dissipated or is currently being masked by other aspects of the atmosphere. A few months later HST discovered a new dark spot in Neptune's northern hemisphere. This indicates that Neptune's atmosphere changes rapidly, perhaps due to slight changes in the temperature differences between the tops and bottoms of the clouds

Neptune also has rings. Earth-based observations showed only faint arcs instead of complete rings, but Voyager 2's images showed them to be complete rings with bright clumps. One of the rings appears to have a curious twisted structure.

Like Uranus and Jupiter, Neptune's rings are very dark but their composition is unknown.

Neptune's rings have been given names: the outermost is Adams (which contains three prominent arcs now named Liberty, Equality and Fraternity), next is an unnamed ring co-orbital with Galatea, then Leverrier (whose outer extensions are called Lassell and Arago), and finally the faint but broad Galle.

Neptune's magnetic field is, like Uranus', oddly oriented and probably generated by motions of conductive material (probably water) in its middle layers.

Neptune can be seen with binoculars (if you know exactly where to look) but a large telescope is needed to see anything other than a tiny disk.