Neptune

Neptune was discovered 65 years after Uranus by two men called Johann Galle and Heinrich Ludwig D'Arrest, althought Galileo had seen it in 1613, he did not realise what it was.

Neptune is located 4.5 billion kilometers from the Sun, that's more than three times as distant as Saturn. It takes 165 Earth years to orbit the Sun. Neptune's diameter is roughly 49,242 kilometers. It's day is only 16.3 Earth hours. Neptune is very much like Uranus in physical composition, primarily a hydrogen, helium, methane and ammonia atmosphere.

When Voyager visited Neptune in 1989, our knowledge about the planet greatly increased. Six moons and four rings were discovered and the existence of a magnetic feild was confirmed. Neptune's mean temperature is -178 degrees C.

The most visually noticable aspect about Neptune is the 'Great Dark Spot' (GDS). Located at a mean latitude of 22 degrees south and with an overall length of 30 degrees longitude, it is very much like the GRS. The Great Dark Spot is an elliptical, stormlike feature that rotated in an anticlockwise direction and is located above the surrounding cloud tops. The GDS completes a revolution of the planet in 18.3 hours, moving east to west.

Neptunes rings are very irregular, and at first were thought to be incomplete arcs. It is now known that there are four thin rings around the planet.