♆ Outer Solar System
Neptune
The edge. The last of the eight.
Neptune is the edge. The last of the eight, so distant that light from the Sun takes over four hours to reach it. From Neptune's surface, the Sun would appear as little more than an unusually bright star. Yet Neptune is not calm — its winds are the fastest in the solar system, reaching 2,100 kilometres per hour. It was not discovered by observation but by mathematics: astronomers predicted its existence before they ever saw it.
"It was predicted by mathematics before anyone ever saw it."
Key Data
Distance from Sun
Light Travel Time from Sun
Peak Wind Speed
Day Length
Confirmed Moons
Orbital Speed
Diameter
Year Length
One Remarkable Thing
Voyager 2 is the only spacecraft ever to visit Neptune, flying past in 1989. It remains the only close-up images we have ever taken. No mission has returned since, and none is currently planned.
Scale Relative to Earth
Neptune's diameter is 49,244 km — about 3.9 times Earth's. At 4.5 billion kilometres away, it took Voyager 2 twelve years to reach it.