Friday 29 January 2016

What shape is the Earth? Find out and let me know!

There’s been a bit of a commotion recently about the shape of the Earth. Some found it funny, but I found it inspirational.

We live in pretty exciting times. We can work out for ourselves exactly what shape the Earth is. We don’t need to rely on scientists: we can be scientists.

To understand the basic principle we can use, let’s consider a situation that’s a bit less planet sized. Suppose you are in a city and you see something interesting. Maybe a car. A unique, one of a kind car: Chitty Chiity Bang Bang.

You obviously phone your best friend to share the excitement. How could you not? He tells you that he can also see Chitty Chiity Bang Bang. So now, thanks to the miracle of telecommunications, you suddenly know something about the position of your friend. You know he must be quite close, because you can both see the same car.

You tell him that Chitty Chiity Bang Bang is about 100 metres away from you. He says that it’s about 50 metres from him. So know you know that he can be no further than 150 metres away. But in what direction?

You tell him that you are standing directly in from of the car. If he says that he is behind, you know that he’s 150 metres right in front of you. If he says that he is to the side of the car, with it pointing towards his right, you know that he is over to your left. With a bit of pythagorus you can work out the distance. With some trigonometry you can work out what angle.

So just because you can talk to each other, and because you can see the same object, each can work out exacty where the other one is. That’s something we’d probably think of as quite obvious. But it’s nevertheless pretty awesome.

What’s this got to do with the shape of the Earth? Well, we can apply the exact same principle. First we need a bunch of friends all over the world. Then we need some object that we can all see. Fortunately, we have a couple to choose from: the Sun and the Moon. The stars could come in handy to.

Get on Skype with your mates to make sure you are all looking at the same thing at the same time. Compare notes on where the Sun is. Don't look at it of course.
It won't do your eyes any favours, and it's not easy to get good measurements like that either. You're better of working out where it is using shadows. Is it directly overhead for some of you, near the horizon for some and not visible for others? What would that imply about the shape of the Earth? You can do the same thing for the Moon, but you can get a bit fancier. If it’s a half moon, what is the angle between the halfway line and the horizon? How does that change for your friends. You could compare the position of Orion’s belt in the sky and its angle to the horizon too. There’s loads of measurements you could make!

Then you can start thinking about what your reslults mean. You can try to work out what shape the Earth would need to be for you to get these results. If you get a bit of maths out, you could even try to work out how big the Earth is, and how far away the Sun is. All using the same techniques as when you worked out where your friend was using Chitty Chitty Bang Bang.

Once you’ve thought about it long enough. You will finally know what shape the Earth is. Not because someone told you. Not because you looked it up. With your own eyes and your own brain you figured out the shape of the Earth. You won’t need to trust anyone’s word on it. You will know it, more deeply and intimately than pretty much everyone else, because you worked it out for yourself.

Let me know what you find out.

This post is not the usual fare for this blog. I am usually talking about quantum error correction, which is more fun than it sounds. The first blog in the series is here