Neptune is so dim and distant that you can only see it with a moderately powerful telescope. But Neptune is the 4th largest planet in the Solar System. Let’s take a look at how big Neptune is, and compare it to some other objects that you might be familiar with.
Neptune is the 4th largest planet in the Solar System, after Jupiter, Saturn, and Uranus. It’s much larger than the terrestrial planets: Mercury, Venus, Earth and Mars.
The diameter of Neptune is 49,500 km. Need some comparison? That’s approximately 3.9 times the diameter of Earth. In other words, you could put almost 4 Earths side to side to match the diameter of Neptune.
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The volume of Neptune is 6.25 x 1013 km3. That’s an enormous number, so once again, for comparison, that’s 57.7 times the volume of Earth. You could fit 57 Earths inside Neptune with room to spare.
The surface area of Neptune is 7.64 x 109 km2. That’s 15 times as much surface area as Earth; of course, Neptune doesn’t have a solid surface, so you wouldn’t want to live there.
The mass of Neptune is 1.02 x 1026 kg. Again, for comparison, that’s the equivalent of 17.1 Earths.
So now, when you look through a telescope and see that tiny blue-green dot, you can get a better sense of the size of Neptune.
We have written many articles about Neptune on Universe Today. Here’s an article about a minor planet found near Neptune. And an article about how Neptune’s south pole is the hottest 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 have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.