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 450 crore 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 field was confirmed. Neptune's mean temperature is -178 degrees C.

The most visually noticeable aspect about Neptune is the 'Great Dark Spot'. It is very much like the Great Red Spot. The Great Dark Spot is an elliptical, storm-like feature that rotated in an anti-clockwise direction and is located above the surrounding cloud tops. The spot completes a revolution of the planet in 18.3 hours, moving east to west.

Neptune’s 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.

While flying past Neptune, Voyager spotted a small white cloud shooting around the planet's upper atmosphere every 16 hours.

It was dubbed ‘The Scooter' because of its strange shape. It may have been a plume rising from a larger cloud lower in the atmosphere. But what is was is still a mystery.