Neptune is one of the two
planets that are not visible without a telescope. Neptune is about 30
times farther from the Sun than is the Earth. Neptune's diameter is about
30,800 miles (49,500 kilometers), or about four times the Earth's
diameter. The planet is about 17 times as massive as the Earth, but
not as dense. Neptune has eight natural satellites (moons).
Astronomers have also observed many rings around the planet.
Neptune has a strange
orbit interlaced with that of Pluto. Every 248 years, Pluto moves
inside Neptune's orbit for about 20 years. During this time,
Neptune is the furthest planet from the Sun. Pluto entered
Neptune's orbit on January 23, 1979 and will
remain there until March 15, 1999.
Besides the strange orbit
of these two planets, Neptune has an elliptical orbit, meaning it
travels in an oval shape around the Sun. The planet's mean distance
from the Sun 2.793 billion miles (4.495 billion kilometers).
Neptune's orbit takes it around the Sun in about 165 Earth-years,
compared to the one year orbit on Earth. As Neptune is orbiting the
Sun, it is also rotating on an axis, which is tilted about 30 degrees.
The axis is an imaginary line running from each pole (north and south).
This axis rotation takes about 16 hours.
Because no orbiters have
brought back samples of the chemical composition of the Neptune
surface, scientists have many theories about the surface of the planet.
They have settled on the hypothesis that the surface is made up of
chiefly hydrogen and helium. Scientists also believe that the interior
of the planet begins with an interior of highly compressed gases that
blend into a central rocky core.
Neptune is surrounded by a
flock of clouds in rapid motion. These clouds are mainly composed of
frozen methane.
A dark area on the surface
of Neptune is thought to be a violent storm of swirling masses of
various gases. This Great Dark Spot is approximately the size of the
Earth.
Neptune has eight natural
satellites, the largest being Triton, about 1,700 miles (2,700
kilometers) in diameter and about 220,000 miles (350,000 kilometers)
from Neptune. Another satellite visible with a telescope is Nereid,
which is only about 210 miles (340 kilometers) across.
The rings of Neptune
aren't as spectacular as the rings of Saturn. They are very faint and
not as brilliantly colored. They are believed to be particles of
dust.
Neptune was discovered by
the use of mathematics before being observed through a telescope.
Astronomers had noticed that Uranus, which they thought was the most
distant planet at the time, was not always in it's predicted
position. They concluded that forces of gravity from another
celestial body were acting upon it. Astronomers got together
and later discovered the eighth planet.
Images of Neptune
Image of the rings on
Neptune.
http://bang.lanl.gov/solarsys/neptune.htm
Zoomed out image of the
dark spot on Neptune.
http://bang.lanl.gov/solarsys/neptune.htm
Zoomed image of The Great
Dark Spot on Neptune.
http://bang.lanl.gov/solarsys/neptune.htm
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