Next Stop Neptune, Please Mind The Gap

The original title of this was What Does 239,000 Miles Look Like?, but as with just about everything I write, it sort of evolved from being a simple question to wondering about the sheer scale of distances involved in our solar system.

It is often hard to imagine and appreciate just how vast space is. Our nearest neighbour that we all see most evenings – the Moon – is on average 239,000 miles away. Or in kilometres, 384,633. But because we all look up, we all know roughly how big the Moon should appear, we don’t really stop and think about it too much.

But to give some sense of perspective, the Earth’s diameter (at the equator) is 7,917.5 miles, or 12,742 kilometres. So you can fit approximately 30 Earths between us and the Moon. And to get there, Apollo 11 left Earth’s orbit at around 7 miles per second, which is about 25,000 miles per hour. It took Armstong, Aldrin and Collins about 52 hours to get there back in 1969.

If you had a ping-pong ball (Earth) and a pea (Moon), you can visually see the distance by moving the pea 2.4 metres away from the ball. That is roughly, to scale, 239,000 miles.

Now, our nearest planetary neighbour is Venus. She is about 77.25 million miles away, or 124 million kilometres. So already we’ve jumped a fair bit, from approximately a quarter-of-a-million miles, to 77 of them. That is 308 times the distance from ourselves to the Moon.

Venus is just about the same size as Earth, so if you had two ping-pong balls… it gets a bit tricky because for a start it is hard to visualise, thus rendering the point of the exercise moot. And well, at some point the curvature of the Earth comes into play and it all gets a bit complicated (but it is approximately 700 metres away, ball-to-ball). Needless to say, our nearest planet is bloody far away.

And visible at the moment. For those in the UK and Western Europe, Venus is in the West just after sunset. Only visible for a couple of hours before setting below the horizon, Venus will appear to your eye has a bright star that you are not used to seeing.

Mars is 154 million miles, or 248 million kilometres, so about twice as far away as Venus, and then after Mars, the distances really start to balloon. The four rocky planets (Mercury, Mars, Venus and ourselves) are actually all quite close to one another. But after Mars and beyond the asteroid belt, we have the largest planet in the solar system, the gas giant Jupiter.

Jupiter is big. Massive. It’s diameter at the equator is 86,880 miles, or 139,820km. That’s more than 10 times Earth’s, and where you can fit 30 of our blue planets between ourselves the Moon, you could only fit 3 Jupiters. But size aside, when we start to look at the gas giants, it is the distance between them that starts to get unfathomable.

Jupiter, from Earth, is 527 million miles, or 848 million kilometres. To put that into perspective, it is 77m miles to Venus, 154m miles to Mars, and then 527m miles to Jupiter. To Saturn… just shy of a billion miles, or 1.6 billion kilometres.

Uranus is 1.8 billion miles (3 billion kilometres), Neptune 2.8 billion miles (4.6 billion kilometres). That’s insane. From us to Saturn is a billion miles, but to get to the next planet, it is another billion. And then, to get to Neptune… another billion.

Earth to Neptune, ball-to-ball – and for the absolute record, this is just guestimation and simple math – about 24,000 kilometres, or 15,000 miles. You can see how the point of the exercise quickly becomes useless when you try and scale it up to the unfathomable size of the solar system.

If we say the Earth is the size of a ping-pong ball, and say Neptune is a tennis ball, you have to move the tennis ball approximately twenty-four thousand kilometres away to judge its relative distance from Earth… to scale.

The above graphic depicts some interesting facts relating to our solar system, most notably for this article is the scale in the bottom-right. Although the graphical depictions of the planet sizes is to scale, their distances relative to each other is not. But in the bottom-right, there is a handy line with relevent markers. The four rockies are basically on top of each other, and then the four gassies are spread out.*

But this is our solar system. I’ve seen Jupiter and Saturn through my telescope. I’ve just-about made out the dot on Jupiter’s surface – her raging storm – and I’m proud to say I’ve just-about made out Saturn’s rings, although a bit of a hazy white line around a hazy white blob. But still, with my own eye pressed up against an eyepiece of a telescope, looking at something a billion miles away.

I have observed the highest planet [Saturn] to be tripled-bodied. This is to say that to my very great amazement Saturn was seen to me to be not a single star, but three together, which almost touch each other. Galileo Galilei

Galileo thought that because he was looking at the planet in a telescope not too disimilar to my own in **capability, and the rings do look a bit furry, almost like the planet has ears – or as Galileo thought – two large moons either side.

Distances in space just boggle my mind, and to know that we are just one system among hundreds of billions in the galaxy, which in itself is just one of hundreds of billions more.

So the next time you look up at the Moon, and as I type she is bright and bold in the sky this evening, just stop and think for a moment. Yes, a familiar object, always there, waxing and waning through the month. But just have a little think as to how far away she really is.

*No one is allowed to mention Pluto. Honestly, let’s just not go there because it is an argument that no one ever wins. But bless the little rock in the Kuiper Belt, she is about 5 billion kilometres away.

**Such is the power of time-over-money, it took 400 years for telescopes of the power and clarity that Galileo used to become affordable to the casual astronomer.

All distances approximate. They obviously vary considerably as the planets orbit and move, and for each I simply Googled the current distances at the time of writing.

Lead photo as taken by the Mars Express on July 3rd, 2003, at a distance of around 5 million miles from Earth and depicts our blue marble on the left and the Moon on the right and approximately 239,000 miles of nothing in between.