Neptune’s Orbit

by Fraser Cain on December 9, 2008

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Neptune seen from Earth. Image credit: Keck

Neptune seen from Earth. Image credit: Keck


Neptune orbits the Sun at an average distance of 4.5 billion km.

That’s the simple answer to the question, what is the orbit of Neptune. However, things are actually a little more complicated than that. Like all the planets in the Solar System, Neptune follows an elliptical path around the Sun, varying its distance to the Sun at different points along its orbit.

At its closest point in its orbit, which astronomers call perihelion, Neptune gets within 4.45 billion km, or 29.77 astronomical units (1 astronomical unit or AU is the average distance of the Earth to the Sun).

At its most distant point in its orbit, called aphelion, Neptune reaches a distance of 4.55 billion km, or 30.44 astronomical units.

One interesting feature about the orbit of Neptune is the fact that Pluto’s very elliptical orbit sometimes brings it closer to the Sun. Back in the days when Pluto was still a planet, it would spend a few decades every orbit closer to the Sun. So Neptune was actually the most distant planet, and Pluto was closer. The last time this happened started in 1979, and ended in 1999. Of course, Pluto isn’t a planet any more, so Neptune’s orbit makes it the most distant planet.

We have written many article about Neptune on Universe Today. Here’s an article with images of Neptune captured by the Hubble Space Telescope. And here’s another discussing the planet’s relatively warm south pole.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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