Neptune is the outermost planet, a deep blue ice giant with the fastest winds in the Solar System, found where mathematics predicted it should be.
At a glance
| radius | 24,600 km (3.86 × Earth) |
|---|---|
| distance from the Sun | 30.1 AU (4.5 billion km) |
| sunlight takes | 4.17 hours |
| one orbit | 165 years |
| orbit eccentricity | 0.0095 |
| reflects | 44% of the sunlight it gets |
Read off the piece’s own catalogue, the same values it draws with.
About Neptune
Neptune is close to Uranus in size and make-up, an ice giant of water, ammonia and methane beneath a hydrogen and helium atmosphere, but its blue is deeper and its weather far more violent. Its winds are the fastest measured on any planet, and it radiates more heat than it receives from the distant Sun, energy left over from its formation that drives its storms.
It was the planet found by calculation. Small irregularities in the motion of Uranus led Urbain Le Verrier to predict where an unseen planet must lie, and Johann Galle, searching at the Berlin Observatory, found Neptune close to that spot. Voyager 2 is the only spacecraft to have visited, and it saw a huge dark storm, the Great Dark Spot, that later disappeared.
Neptune has faint, clumpy rings and a large moon, Triton, which orbits it backwards. Beyond Neptune lies the Kuiper belt, the cold realm of Pluto and countless other icy bodies.
What you see in the piece
This far from the Sun, Neptune is lit by a much dimmer sunlight than Earth gets, so it appears as a faint blue disc. It is too faint to see from Earth without a telescope, and from another star it cannot be seen at all.
Questions
How was Neptune discovered?
By prediction. Irregularities in the orbit of Uranus led Urbain Le Verrier to calculate where an unseen planet should be, and Johann Galle found Neptune near that position through a telescope.
How far is Neptune from the Sun?
Neptune is 30.1 AU (4.5 billion km) from the Sun, so sunlight takes 4.17 hours to reach it.