Hi. For most of human history, we've been stuck here on the surface of this planet. To do astronomy, we need to look up through the atmosphere, to catch the light from the stars coming down through the atmosphere. Unfortunately, a lot of the most exciting science can only be done by getting above that atmosphere. I'm going to show you three pictures that are examples of this. So this first picture here, is a cluster of galaxies. And in between the galaxies, there's very hot gas. It's so hot it's emitting x-rays. But those x-rays are blocked by the atmosphere. They don't get through. Here's another picture. This is a starburst galaxy. This galaxy is making thousands of new stars every year. But all those stars are buried inside dust clouds, and the light comes out in the far infrared. The far infrared gets blocked by the atmosphere, it does not get through. Here's a third picture. This is an artist's impression of an x-ray binary. That's one normal star and one collapsed star, a black hole. Material is being pulled off the normal star, is falling onto the black hole. And as it falls onto the black hole it gets very hot. It get's so hot it emits x-rays again, and the x-rays are blocked by the atmosphere, they don't get through. So, to do any of those pieces of science, we need to get above the atmosphere. It's impossible any other way. Right. So astronomers hate the atmosphere. It's a big problem for us. We can do much more exciting science if we get above it. So, what is so bad about the atmosphere? Well there are three things. The first is what we've been concentrating on so far, that it blocks a lot of the light we want to detect. It just happens that objects in the universe emit x-rays far infrared, ultraviolet, things that don't get through the atmosphere. So, to do that sort of science we simply have to get above the atmosphere. There's no alternative. There's a second problem, and that is that the atmosphere distorts light. Now the light is not quite smooth. I'm sorry, the air is not quite smooth. It has pockets of of gas. Some of which are denser than others. As the light comes down through the atmosphere, and it hits pockets of different density it gets refracted. Just like light going from the air to water. You hit a different density, the light is refracted, it gets bent. So, as the light comes down through the atmosphere it wiggles about like this - by a very small amount, but it's enough to smear out our pictures. The pictures are blurred, they're not as sharp as they can be, if we get above all that, into space. There's a third problem, which is maybe not quite so obvious at first. If you look at a city like Edinburgh behind me here - we are in day time here obviously, but at night time, it's just full of street lights. The light from the streetlights shines up into the sky, scatters from the atmosphere and comes back down - so the sky actually looks bright. It makes a glare, that makes it hard to see faint objects. Now, even if you get well away from cities, out into the country side, distant regions, the sky's never quite completely dark. Particles coming from the sun, the solar wind, hitting the Earth's atmosphere, excite it and you get air glow. Now this is very pretty. It's what makes the Northern Lights that we can see at polar latitudes. Very beautiful, but astronomers hate it. To us, it's just a nuisance. So, those are the three reasons that astronomy, that, that the atmosphere is a problem for astronomy. So, we want to go up into space. But it's not easy to do.