Neptune is the furthest planet from the sun,in the solar system.It is situated at an average distance of about 4,500 million kilometres.It is a gas giant and is thought to consist of a small rocky core surrounded by a mixture of liquids and gases. The atmosphere contains several prominant features of clouds. The largest of these are the Great Dark Spot,and the Scooter.The Great and Small Dark Spots are huge storms that are swept around the planet by winds of about 2,000 kilometres per hour. The Scooter is a large area of cirrus cloud. Neptune is an ice giant that has the same deep, blue color like Uranus. Neptune gets its color from the methane in the atmosphere. The dark spots on Neptune are from the storms that happen on the planet. Neptune has the same seasons as Earth, but Neptune's spring lasts for 40 years. Most of Neptune's energy lies inside the planet. The chemicals change into a different form of energy when deep beneath the surface. It releases a ton of heat when the change occurs. The atmosphere contains about 80% hydrogen, 19% helium and 1% methane. Neptune's length of day is 16.11 hours and the year length is 169.9 Earth days. Neptune weighs about 105 669 X 10 to the power of 19kg. That weighs heavier then Earth right? Neptune's cloud gravity is 1.13g and the diameter from the middle of the planet is 49,532km. The distance from Neptune to Earth is 248 light minutes away.(Distance used in space) The most dangerous thing about Neptune is that it has extreme winds in the atmosphere. Neptune was thought to have no rings but in 1989, rings were discovered by Voyager 2 spacecrafts. The discovery of Neptune was made from a person named Galileo Galilei. He made his first drawing of Neptune on December 28, 1612. Thinking it was a fixed star when it appeared to the eye. During the period of Galileo first observation, Neptune was stationary in the sky because it turned retrogradethat day. This appeared in a backward motion when the orbit of Earth takes it path out of order. However, in 2009 University of Melbourne, David Jamieson got proof and told everyone his new evidence saying that Galileo was not aware of the fixed star. It was actually a planet, Neptune.
Once Uranus was discovered, astronomers set about charting its orbit. The figures we have just listed do indeed describe Uranus's orbital motion, but eighteenth-century astronomers quickly discovered a small discrepancy between the planet's predicted position and where they actually observed it. Try as they might, astronomers could not find an elliptical orbit that fit the planet's trajectory to within the accuracy of their measurements. Half a century after Uranus's discovery, the discrepancy had grown to a quarter of an arc minute, far too big to be explained away as observational error. The logical conclusion was that an unknown body must be exerting a gravitational force on Uranus--much weaker than that of the Sun, but still measurable. But what body could this be? Astronomers realized that there had to be another planet in the solar system perturbing Uranus's motion.
In the 1840s, two mathematicians independently solved the difficult problem of determining this new planet's mass and orbit. A British astronomer, John Adams, reached the solution in September 1845; in June of the following year, the French mathematician Urbain Leverrier came up with essentially the same answer. British astronomers seeking the new planet found nothing during the summer of 1846. In September, a German astronomer named Johann Galle began his own search from the Berlin Observatory, using a newly completed set of more accurate sky charts. He found the new planet within one or two degrees of the predicted position--on his first attempt. After some wrangling over names and credits, the new planet was named Neptune, and Adams and Leverrier (but not Galle!) are now jointly credited with its discovery.
Neptune orbits the Sun with a semi-major axis of 30.1 A.U. (4.5 billion km) and an eccentricity of just 0.01. Since its sidereal orbital period is 164.8 years, it has not yet completed one revolution since its discovery. Unlike Uranus, Neptune cannot be seen with the naked eye, although it can be seen with a small telescope--in fact, Galileo may actually have seen Neptune, although he had no idea what it really was at the time. Through a large telescope, Neptune appears as a bluish disk, with a maximum angular diameter of 2.4´´ at opposition.
Neptune is so distant that surface features are virtually impossible to discern. Even under the best observing conditions, only a few markings can be seen. These are suggestive of multicolored cloud bands--light bluish hues seem to dominate. With Voyager 2's arrival, much more detail emerged, at least, Neptune resembles a blue-tinted Jupiter, with atmospheric bands and spots clearly evident. From Earth, we can see only two moons orbiting Neptune. William Lassell discovered the inner moon, Triton, in 1846. The outer moon, Nereid, was located by Gerard Kuiper in 1949. Voyager 2 discovered six additional moons, all less than a few hundred kilometers across and all lying within Nereid's orbit.
In its moons we find Neptune's contribution to our list of solar system peculiarities. Unlike the other jovian worlds, Neptune has no regular moon system. The larger moon, Triton, is 2800 km in diameter and occupies a circular retrograde orbit 354,000 km (14.2 planetary radii) from the planet, inclined at about 20° to Neptune's equatorial plane. It is the only large moon in our solar system to have a retrograde orbit. The other moon visible from Earth, Nereid, is only 200 km across. It orbits Neptune in the prograde sense, but on an elongated trajectory that brings it as close as 1.4 million km to the planet and as far away as 9.7 million km. Nereid is probably similar in both size and composition to Neptune's small inner moons.
Voyager 2 approached to within 24,000 km of Triton's surface, providing us with essentially all that we now know about that distant, icy world. Astronomers redetermined the moon's radius (which was corrected downward by about 20 percent) and measured its mass for the first time. Along with Saturn's Titan and the four Galilean moons of Jupiter, Triton is one of the six large moons in the outer solar system. Triton is the smallest of them, with about half the mass of the next smallest, Jupiter's Europa.
Lying 4.5 billion km from the Sun, and with a fairly reflective surface, Triton has a surface temperature of just 37 K. It has a tenuous nitrogen atmosphere, perhaps a hundred thousand times thinner than Earth's, and a surface that most likely consists primarily of water ice. The moon's low temperatures produce a layer of nitrogen frost that forms and evaporates over the polar caps, a little like the carbon dioxide frost responsible for the seasonal caps on Mars. Overall, there is a marked lack of cratering on Triton, presumably indicating that surface activity has obliterated the evidence of most impacts. There are many other signs of an active past. Triton's face is scarred by large fissures similar to those seen on Ganymede, and the moon's odd cantaloupe-like terrain may indicate repeated faulting and deformation over the moon's lifetime. In addition, Triton has numerous frozen "lakes" of water ice which are believed to be volcanic in origin. Triton's surface activity is not just a thing of the past. As Voyager 2 passed the moon, its cameras detected two great jets of nitrogen gas erupting from below the surface, rising several kilometers into the sky. it is thought that these "geysers" result when liquid nitrogen below Triton's surface is heated and vaporized by some internal energy source, or perhaps even by the Sun's feeble light. Vaporization produces high pressures, which force the gas through cracks and fissures in the crust, creating the displays Voyager 2 saw. Scientists conjecture that nitrogen geysers may be very common on Triton and are perhaps responsible for much of the moon's thin atmosphere.
The event or events that placed Triton on a retrograde orbit and Nereid on such an eccentric path are unknown, but they are the subject of considerable speculation. Triton's peculiar orbit and surface features suggest to some astronomers that the moon did not form as part of the Neptune system but instead was captured, perhaps not too long ago. Other astronomers, basing their views on Triton's chemical composition, maintain that it formed as a "normal" moon but was later kicked into its abnormal orbit by some catastrophic event, such as an interaction with another similar-sized body. It has even been suggested that the planet Pluto may have played a role in this process, although no really convincing demonstration of such an encounter has ever been presented. The surface deformations on Triton certainly suggest fairly violent and relatively recent events in the moon's past. However, they were most likely caused by the tidal stresses produced in Triton as Neptune's gravity circularized its orbit and synchronized its spin, and they give little indication of the processes leading to the orbit in the first place.
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