Neptune Fact Sheet

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The following Neptune fact sheet is based on NASA’s excellent planetary fact sheets. Neptune is the 8th planet from the Sun, and it requires a telescope to be able to see it.

Mass: 102.43 x 1024 kg
Volume: 6,254 x 1010 km3
Average radius: 24,622 km
Average diameter: 49,244 km
Mean density: 1.638 g/cm3
Escape velocity: 23.5 km/s
Surface gravity: 11.15 m/s2
Natural satellites: 13
Rings? – Yes
Semimajor axis: 4,495,060,000 km
Orbit period: 60,189 days
Perihelion: 4,444,450,000 km
Aphelion: 4,545,670,000 km
Mean orbital velocity: 5.43 km/s
Orbit inclination: 1.769°
Orbit eccentricity: 0.0113
Sidereal rotation period: 16.11 hours
Length of day: 16.11 hours
Axial tilt: 28.32°
Discovery: 23 September 1846
Minimum distance from Earth: 4,305,900,000 km
Maximum distance from Earth: 4,687,300,000 km
Maximum apparent diameter from Earth: 2.4 arc seconds
Minimum apparent diameter from Earth: 2.2 arc seconds
Maximum visual magnitude: 7.78

We’ve written many articles about Neptune for Universe Today. Here’s an article about the color of Neptune, and here’s an article about the atmosphere of Neptune.

If you’d like more info on Neptune, check out Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We’ve also recorded an entire episode of Astronomy Cast just about Neptune. Listen here, Episode 63: Neptune.

How Far is Neptune’s from the Sun?

Neptune’s distance from the Sun is 4.5 billion km; more specifically, it’s 4,503,443,661 km. If you’re still using the Imperial system, that’s the same as 2.8 billion miles.

But this number is actually an average. Like all of the planets in the Solar System, Neptune follows an elliptical orbit around the Sun, so it’s sometimes closer and sometimes further than this average number. When Neptune is at its closest point to the Sun, called perihelion, it’s 4.45 billion km from the Sun. And then when it’s at its most distant point from the Sun, called aphelion, it’s 4.55 billion km from the Sun.

Astronomers also measure distance in the Solar System using a measuring tool called the “astronomical unit”. 1 astronomical unit, or AU, is the average distance from the Earth to the Sun; that’s about 150 million km. So, Neptune’s average distance from the Sun is 30.1 AU. Its perihelion is 29.8 AU, and it’s aphelion is 30.4 AU.

We have written many articles about Neptune for Universe Today. Here’s an article about Neptune’s moons, and here’s an article about how Neptune’s southern pole is the warmest place on the planet.

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’ve also recorded an episode of Astronomy Cast all about Neptune. Listen here, Episode 63: Neptune.

How Long Does it Take Neptune to Orbit the Sun

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Neptune orbits much further away from the Sun than the Earth, so its orbit takes much longer. In fact, Neptune takes 164.79 years to orbit around the Sun. That’s almost 165 times longer than Earth takes to orbit the Sun.

Here’s an interesting fact. Neptune was only discovered on September 23, 1846. At the time this article was written (2009), that was only 163 years ago. In other words, since its discovery, Neptune has not even made a single orbit around the Sun.

On July 11, 2011, Neptune will have completed one full orbit around the Sun. Finally, Neptune will be 1 year old.

Just like Earth, Neptune’s axis is tilted away from the Sun’s axis. This means that it experiences seasons as it orbits the Sun. For half of its orbit, Neptune’s northern hemisphere is tilted towards the Sun, and then for the second half of its orbit, its southern hemisphere is tilted towards the Sun. This differential heating creates very powerful winds on Neptune. In fact, Neptune has the strongest sustained winds on the Solar System, with winds measured at 2100 km/hour.

We have written many articles about Neptune for Universe Today. Here’s an article about the atmosphere of Neptune. And here’s an article about who discovered Neptune.

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 also recorded an entire episode of Astronomy Cast just about Neptune. Listen here, Episode 63: Neptune.