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# Podcast: Is the Earth flat, or a circle?

Well, first things first a circle is a two-dimensional shape, so a circle is definitely flat. Listen to the mini-podcast below to hear more from Mat Disney.

25 October 2023

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## Transcript

ROBERTA LIVINGSTON: Hello and welcome to Ask the Expert where you ask the questions and UCL's finest experts answer. I'm your host, Roberta Livingston. I'm a schools engagement assistant at UCL East and on today's episode, you'll be hearing from Mat Disney, Professor of Remote Sensing in the Geography department at UCL. He is responding to the question is the Earth flat or a circle? Let's hear what he has to say…

MAT DISNEY: OK, alright. So question is, is the Earth flat or is it a circle? And obviously the first thing we can say is that it's neither of those things because it's a 3 dimensional object. So even if it were flat, which is not, then it wouldn't be a circle. It could take on any number of different shapes, but it's not flat so the I guess the the question is, is, is it a sphere or is it flat? And how do we if it is a sphere, how do we know it's a sphere? Now the simple answer to that is, you know, essentially we can go into space now and we can take a photo looking back and we can see that the Earth is, you know, close to a sphere. We can watch it rotating. We can see it passing underneath. So we've known ever since we've been able to put satellites in space and cameras in space that we can see the Earth as a sphere. I say it's not quite a sphere. It's a little bit squashed because it swells out at the because it's spinning quite fast, it swells out a bit at the equator, so it's a little bit of a kind of flat that I could imagine a a football and you're just pressing down a little bit on the top of it. So it's a bit wider at the equator than it is than it is at the poles, but let's say it's a sphere. OK, so we can tell straight away that we know it's it's not flat, it's not a circle, it's a sphere. We could see it rotating. There's all sorts of other reasons why that. we know it's a sphere one of those reasons that that we notice sphere is cause we can see things in the distance on a on a very flat horizon. For example on the surface of the ocean we can watch objects appear out of apparently out of nowhere as they come towards us. So we can see them essentially coming over the horizon now. You know, one of the questions would be, well, why can't I see the kind of curvature of the earth at the horizon? And the answer to that is you need to be able to see a very long way in either side to be able to see that because the earth is so large compared to us standing on. the surface. You'd need to be able to see a horizon stretching for 10s and 10s and 10s of kilometres from your left to your right to be able to see that effect. If you go up a bit higher and you have a perspective, you know if you're on a on a high mountain or in an aircraft, then you can start to see that curvature. Because you can see hundreds and hundreds of kilometres straight out spread out below you so we can start to see that. But when we're down on the Earth surface, it looks very, very flat because for kilometres in all direction, it is essentially flat and things get in the way. A hedge is not flat. It's gonna get in the way of us seeing the horizon. You know any little bumps and lumps so we need to find somewhere really, really flat. We need to be able to see 20, 30, kilometres in in away from us and 20, 30, 40, 50 kilometres either side of us. Then we can start to see that curvature and pretty much the only place you can see that realistically is on the surface of the ocean. And so that's why surface of the ocean, you can start to see things like ships in the far distance appearing up over the horizon. Or conversely, if they're going away from you disappearing over the horizon. So there's there's a kind of there are ways to see that, you know.

Image Credit: Quora.