The Canadian Space Agency observatory took this image of Neptune and Triton on August 31, 2006, at about 00:45 UTC.

On August 24, 2006, the International Astronomical Union adopted a new definition of a planet, and Pluto was demoted to the ranks of a dwarf planet. This means Neptune, the eighth planet, now has the distinction of being the farthest in our solar system.

Neptune was officially discovered in 1846 after astronomers observed the strange behaviour of Uranus's orbit, and deduced the planet's existence mathematically. Neptune is therefore the only planet that was discovered by mathematical prediction. For students struggling with their math homework, this is more proof that math matters!

The fourth largest planet in size, and the third largest in mass, Neptune is an ice planet; it's made up of both water and hydrocarbon ice, with a hydrogen, helium, and methane atmosphere. On average, it is more than 4.5 billion kilometres away, or over 30 times the distance between the Earth and the Sun. Like Jupiter, Neptune has a large spot on its surface, possibly a huge, semi-permanent storm. Like Saturn, it has a faint ring.

Neptune currently has 13 known moons, of which Triton is the largest with a diameter of 2,700 kilometres. Triton's orbit is retrograde, that is, it orbits in a direction opposite to the rotation of the planet, which means that it may at one time have been an asteroid or a minor planet that was captured by Neptune.