How far away is Neptune right now?

4,348,007,893

kilometres · Neptune's distance from Earth

About 29 times the distance from Earth to the Sun.
An airliner at cruising speed would take 547 years to cover it.

Right now Neptune is in the evening sky, after sunset. You need a telescope to see it.

Right now Neptune is about 4.3 billion kilometres from Earth, and the gap changes every second. A radio message, moving at the speed of light, needs 4 hours to cross it.

Neptune is the eighth and farthest planet from the Sun, a blue ice giant found by calculation before it was seen. Its distance from us swings between 4.3 billion and 4.7 billion kilometres. The next close approach is on 27 September 2027.

Time until Neptune's next close approach to Earth

331 d 14 h 39 m 55 s

Measured

Temperature of Neptune at the 1 bar level

-201 °C

Measured, with error

Time since Neptune was discovered

180 y 37 d 2 h

Measured

Time since Voyager 2 flew past Neptune

37 y 66 d 16 h

Measured

What is Neptune?

The farthest planet

Neptune is the eighth planet from the Sun, and the farthest. It circles about 30 times as far out as Earth does. Even sunlight needs 4.2 hours to get there. NASA says high noon on Neptune would look like dim twilight to us.

Like Uranus, it is an ice giant. Most of it is a hot, dense fluid of water, methane and ammonia over a small rocky core. Above that is a deep atmosphere of hydrogen and helium, with no solid surface beneath it. Scientists think an ocean of very hot water may lie under the cold clouds, kept from boiling by the crushing pressure.

Neptune is about 3.9 times as wide as Earth, and about 59 Earths would fit inside it. It is a little narrower than Uranus but heavier, with 17 times Earth's mass. Of the giant planets, it is the densest.

Methane in its air takes the red out of sunlight, so Neptune looks blue.

49,528 kmEquatorial diameter of Neptune

The next close approach

Why the distance keeps changing

Earth and Neptune both circle the Sun, like runners on a track. Earth runs fast on an inside lane. Neptune is on the outermost lane of all, and moves so slowly that Earth passes it about once a year.

Each time, Earth lies between the Sun and Neptune, and the two planets are as close as they get. Astronomers call this line-up an opposition. Half a year later Neptune is beyond the Sun, and the gap has grown by roughly the width of Earth's own orbit.

Neptune has crept on a little in the meantime. So the meetings come about every 367 days, a couple of days later in the calendar each year. The clock on this page counts down to the next one, on 27 September 2027.

Neptune is so far away that the swing hardly matters. Even at its nearest, it is about 29 times as far from us as the Sun is.

331 d 14 h 39 m 55 sTime until Neptune's next close approach to Earth

Right now

A hello that takes hours

Radio waves are a kind of light, and nothing travels faster. Even so, a message to Neptune needs 4 hours at today's distance. An answer needs as long again to come back.

Only one spacecraft has ever been there. Voyager 2 skimmed over Neptune's cloud tops on 25 August 1989, the closest of all its planet flybys. It found a restless world: white clouds of frozen methane, fierce winds and a great dark storm. The team boosted the colours of many of its pictures to bring out the clouds, so Neptune looked a deeper blue than it is. Re-processed in 2024, it looks much like Uranus.

It also passed Triton, Neptune's largest moon, and saw geysers of icy material rising from its frozen surface. No spacecraft has been back since. Almost everything we know of Neptune up close comes from those few days.

4,348,007,894 kmNeptune's distance from Earth

23 September 1846

Found by mathematics

Neptune is the first planet found by calculation rather than by searching the sky. Uranus was not moving quite as astronomers expected. Something unseen seemed to be pulling on it.

The French mathematician Urbain Le Verrier worked out where an unknown planet would have to be, and how heavy, to explain the drift. He sent his prediction to Johann Galle at the Berlin Observatory. Galle found Neptune on his first night of searching, on 23 September 1846. Its largest moon, Triton, was found a few weeks later.

Galileo had seen it long before, in 1612 and 1613, but took it for a star.

Neptune takes about 165 Earth years to go once round the Sun. That is about 2.2 human lifetimes. So only in 2011 did it finish its first full lap since Galle saw it. Its tilt is close to Earth's, so it has real seasons, each lasting about 41 years. Its day is short by comparison. With no ground to stand on, a day there is one turn of the planet: 16 h 06 m 36 s.

180 y 37 d 2 hTime since Neptune was discovered

Where the air presses like ours

Winds and cold

Neptune has no surface to stand on, so scientists take its temperature where its air presses as hard as ours does at sea level. There it is about -201 °C. Earth's average is 15 °C.

Yet this cold, dim world has the fastest winds of any planet. NASA calls it the windiest world in the solar system. Clouds of frozen methane race across it at up to about 580 metres per second.

That is about 2.3 times as fast as an airliner, and about 1.7 times the speed of sound in our air. Earth's strongest winds don't come close.

All this on a planet that gets so little energy from the Sun. Its winds even outrun Jupiter's, though Jupiter is far nearer the Sun.