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The Farthest Planet in the Solar System: How Far is Neptune from the Sun?

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How Far is Neptune from the Sun

Let’s start with the simple facts in Astronomy 101 – which planet is closest to the Sun and which farthest? The first title goes to Mercury, but the last one – to the gas giant Neptune. Until 2006, this honorary place belonged to Pluto, but recent planetary classification and a few additional discoveries have led astronomers to believe it is a minor, aka a dwarf, planet. 

Today, the farthest planet from the Earth is the eighth one – Neptune. This planet is so far away that when you try to look at it through a telescope, you will only see a tiny blue-green disk. But how far is Neptune from the Sun? With your own two eyes, you can’t see Neptune from Earth, but with technologically advanced telescopes, you can study it, even if not in detail. This distance has been calculated many times, and now, it is our turn to find out – starting with a few other facts about our planetary home system!

What is the distance from the Neptune to the Sun?

Neptune’s distance from the Sun is not static because planets do not have perfectly round orbits. Instead, they travel in ellipses –  their closest point is called a perihelion, while the farthest is an aphelion. On average, Neptune’s distance to our Sun is 4.5B km or 30AU. It takes over four sunlight hours to get from the Sun to Neptune.

Orbital Today says that reaching Neptune from the Sun would be equivalent to 24,000 flights from Glasgow to Sydney! And, assuming we wanted to take that plane, we would have to stay onboard for 130 years! However, this is a minor trip on the scale of our system. Distance from the Sun to Neptune in light years is only 0.00047 light years, which means the sunlight reaches this planet in only 4.2 hours.

Since it has an average orbital speed of 5.43 km/s, Neptune takes about 164.8 years or 60,182 terrestrial days to complete one full revolution. From our home planet, the average distance to Neptune is 4.5868B km.

How far is Neptune from the Sun at its farthest?

Neptune as the farthest planet, or to be more precise, in its aphelion, lies 4,536,870,000 km from the Sun. But this planet still stands farthest from our star even at its closest point.  Neptune is a completely frozen world because it’s the farthest from the Sun. Nevertheless, scientists believe that there’s a super-hot water ocean underneath its cold clouds and that extremely high pressure keeps this ocean locked inside. 

Do rays ever reach Neptune?

Neptune planet

Since Neptune is far from its main star, many people are wondering if our Sun’s rays ever reach this planet. They do, but very slowly. This blue giant receives 900 times less energy than our Earth. Since light travels at a speed of 300 km/s and doesn’t have mass, it doesn’t reach distant objects like the planet Neptune instantly. For example, a sunray takes 8 minutes and 20 seconds to reach Earth, but for Neptune, it takes 14,950 s or 4.15 h to reach this planet.

Neptune is always dark and cold not only because of this distance and position but also because of the albedo or reflective power. Since its albedo is about 0.29, it reflects just 29% of the light hitting it. Its deepest atmospheric gases don’t only scatter light but also absorb it.

What Else Makes Neptune Unique: More Astronomy Facts

The farthest planet also happens to be one of the largest, with roughly a 24,622 km radius. It’s about four times wider than our planet and has six moons instead of one, like we do.

Because it’s too far from its parent star, Neptune is very cold, and all liquid there is completely frozen. And yet, there are colder planets – for example, Uranus. Still, Neptune’s ‘brand’ blue colour which has given the planet its name associated with the Roman Sea God, is not related to ice. It is an optical illusion that only allows blue colour wavelengths to pass through the atmosphere.

If that’s not unwelcoming enough, think about strong winds raging on Neptune’s surface – sometimes to 2,000 km/h! They are nine times stronger than on Earth and three times stronger than on Jupiter – one more windy destination in our solar system.

Finally, Neptune has a gaseous surface instead of a solid one, so we will not even be able to step on it – not in the classic meaning of this word. So, as far as our space colonization dreams go, Neptune is certainly not the first destination on our to-travel list!

So, is Neptune the farthest planet in the solar system? Indeed, it is!  This will remain so until the Astronomical Union changes its classification of planetary definition – and if this happens, Pluto might yet regain its title. But that is a story for another time – so stay tuned for more space knowledge in our future posts!

Article by Emma Thorpe

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