 I is Brad here at ANU and in astronomy we do a lot with light, how we discover and what we understand the universe. I'm here with Lish from ABC Canberra and Abby and Caitlin and they're going to show us how we actually use light in astronomy. Yeah, so the white light that we see from the sun and from light bulbs is actually broken up into a lot of different colors that we can't see. We can demonstrate that right here with these three torches. We've got the primary colors, blue, red and yellow. Do you hold that Lish? And you hold that one Caitlin. So when we shine it on the table we can see that there's three different colors but when we move it together they create white light, yeah. So what is something in nature that has a lot of different colors? What does it remind you of? A rainbow. Yeah, so a rainbow is like nature's spectrum. After a rainfall the water drops in the atmosphere break up the white light from the sun into a lot of different colors. So how can we use a spectra to understand more about space? Yeah, well that's an interesting question. So we attach this instrument which is a spectroscope to our telescopes. We look at far away objects like the sun like a star and we can see what they're made of. We actually have an example of that here to show you. So as you can see here, this is actually the spectrum of the sun. So you can see the entire rainbow going down here but do you notice anything kind of strange about it? Yeah, there's a lot of color but lots of black lines like a grid. Yeah, exactly. And those black lines are actually because the sun is surrounded by a layer of gas. It's called the photosphere. It's a bit like the atmosphere that surrounds our own earth. And what happens is when the light leaves the core of the star it actually crashes into that photosphere, the gas surrounding and gets trapped. Some of the light doesn't make it to earth and those black lines that you see are actually gaps in the spectrum where the light hasn't got out, the light's actually missing. What we know is that every element has its own unique pattern of these dark lines. So we can analyze this entire pattern of all the different gases in the photosphere, compare them to what we know about the periodic table and figure out what it's made of. So every single element has a spectrum, a bit like a fingerprint. Every individual has a fingerprint. Exactly. So it's a bit like we're looking up someone's fingerprint in the database and we can see who it belongs to. So we can actually look at this as if we were in a lab. So here is our gas bulb. It's got some mercury in it. Have a look through and you can see the spectrum of mercury. Yeah, what do you see in there, Tos? Everything is black, unlike this. And I see a line of orange, a line of green and a line of that indigo blue. Yeah, so that's because there's actually two types of spectrum. This is called an emission spectrum. It's where the object, in this case, mercury emits the light itself. And that's different to an absorption spectrum, like we talked about with the sun, where the element, whatever it happens to be, could be mercury, is absorbing and blocking parts of the light. So how else can we use this spectra to study astronomy? Yeah, well, using the combination of the two different kinds of spectra, we can look at so many different things in the universe. We can look at nebulae, giant clouds of dust and gas and they give off emission spectra. We can look at a star, which gives us absorption spectra, or planets and galaxies, which have both. You know, we can look at the atmosphere of a faraway planet, see if it might have elements to support life. We can look at where stars are born, where they die, how galaxies move. Just so many different things. So you can really see that spectra is one of the basis of astronomy and it's really the key to making discoveries in space. Cool.