Neptune
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Neptune is the eighth planet from the Sun.
Its distance from the Sun is 4, 504, 000 000 km.
Neptune is the fourth largest planet by diameter, it is
smaller in diameter but larger in mass than Uranus.

Neptune was first observed by Galle and d'Arrest
on 23 Sep 1846, but more than two centuries earlier in 1613, Gallileo saw the planet when it was close to Jupiter but thought it was another star. On two consecutive nights he noticed a slight shift in its position against a nearby star, but on the following nights it was out of his field of view.

Because Pluto's orbit is so eccentric, it sometimes crosses Neptunes path, thus making Neptune the most distant planet in the solar system for a few years. Like the other gas planets, Neptune has very strong winds and massive storms. The winds are stronger than on any of the other planets in the solar system, reaching 2000 km/hr.
Only one spacecraft has visited Neptune, Voyager 2 on 25 Aug 1989.
At the time of the Voyager encounter, the most prominent feature on Neptune was the "Great Dark Spot" in the southern hemisphere.
It is about half the size of Jupiter's "Great Red Spot", about the same size as the Earth. Neptunes winds blew the "Great Dark Spot" across the planet at 700 mph. Voyager also observed a smaller dark spot in the southern hemisphere and a small irregular white cloud that zips around Neptune about every 16 hours, known as "The Scooter".

The Great Dark Spot

The Scooter
In 1994 the Hubble Space Telescope observed that the
"Great Dark Spot" has disappeared. It has simply dissipated or is being hidden by some other aspect of Neptunes atmosphere. HST also observed a new dark spot in the northern hemisphere, which indicates Neptunes atmosphere changes rapidly,possibly due to slight variations in temperature between the tops and bottoms of the clouds.
Neptune has eight moons, seven small ones and Triton which is by far the largest.
Only Triton and Nereid were known prior to the Voyager mission.

Triton

Neptune on Triton's
horizon

Montage of Triton
and Neptune

MOON

NAIAD
THALASSA
DESPINA
GALATEA
LARISSA
PROTEUS
TRITON
NEREID

DISTANCE from NEP/km

48 000
50 000
53 000
62 000
74 000
118 000
355 000
5 509 000

DISCOVERER

VOYAGER 2
VOYAGER 2
VOYAGER 2
VOYAGER 2
VOYAGER 2
VOYAGER 2
LASSELL
KUIPER

DATE

1989
1989
1989
1989
1989
1989
1846
1949