 So, Ted, how do you see all those stars and things in the sky? Well, these objects give out light, but lots of different colours of light, including lots of colours that we can't see. Wait, there are colours of light that we can't see? Yes, so we see all the colours of the rainbow, from red to yellow to green to blue and purple, but there are other colours too. So you've heard of x-rays, and these let you take pictures of the bones inside your body, but we can't actually see the x-rays. So x-rays are a colour of light that we can't see. Another colour of light we can't see is microwave light. So you'll have heard of microwaves. Microwaves are used to cook food in microwave ovens. I look at another colour of light which we call gamma rays. Some objects in the night sky give out this colour of light, and we want to learn more about these things by looking at the gamma rays they give out. So, is it these gamma rays that you take pictures of? Yes, in a way, but not quite. These gamma rays travel through space and reach the Earth, but when they touch the Earth's sky, they interact with it. When the gamma ray interacts with the sky, it makes a lot of particles which have loads of energy and are really excited, and these rain down onto the ground from the sky. So, what are particles? Particles are just teeny tiny little blobs, much smaller than a grain of sand or dust. When we put them all together, make up everything you can see, like the ground, clouds, even you and me. Oh, OK. Wow. So yes, these particles move really fast. Now, the fastest thing in the universe is light. It's so speedy that in just one second, it could go around the Earth seven and a half times. That's amazing. Light can go at this super-fast speed when it travels through empty space. But when light goes through air, it travels a little bit slower because the air is in the way, so slows it down a little. Now, these mega-fast particles I was talking about earlier, they go so fast that they travel faster than light in air. And these really fast-moving particles are so speedy that they make a flash of blue light, which we call Turenkov light, after the scientists who found it. The effect is just like the wake of a boat. When the boat is moving, it makes waves. The waves move out from the boat in a circle shape. As the boat moves faster, the waves in front of the boat start to get all bunched up. Then, when the boat moves through the water faster than the speed of the waves it is making, it creates a wake. This means you get a V shape which follows behind the boat. We call this a shock wave. For gamma rays, those super-fast particles that are made when the gamma rays interact with the sky travel faster than light does in air. This makes a shock wave of light that we call Turenkov light. The Turenkov light is what my friends and I look for. I didn't realise so much was going on in the sky above us. That's really interesting, Ted. Yeah, really interesting. I didn't know all that. A lot to take in. I think it might be time for Little Bear and I to head back and get some sleep though. Thanks, Ted. See you again soon.