Neptune, the eighth planet from the sun, is the smallest of the gas giants, and the farthest from the Sun.
Its discovery, in 1846, came about through mathematical calculation, rather than simple observation.
We knew little about Neptune before 1989, when the spacecraft Voyager 2 began photographing it.
Voyager could observe only the southern hemisphere, as the northern was covered in darkness.
This relatively small, bright blue planet is simply just too far away for detailed observation from Earth.
The Voyager photographs revealed some similarities to Neptune’s neighboring gas giants.
It has a varying rotational speed, strong winds, several distinct dark and light spots on its surface, an internal heat source, rings, and moons.
