G'day, I'm Phil Dooley. I'm a science communicator at the research school of physics at A&U. And I hope you know what this image is. These days in light pollution sometimes you don't see that very much, but that, ladies and gentlemen, is the sky. It's beautiful. That's the whole sky put into one image. That's what we've been looking at since we evolved eyes. It's beautiful, it's inspiring, it's mysterious. Originally people just didn't know what these dots of light were. Gradually it was understood that they were stars, didn't really know how far away they were, what made them glow. And there's quite a tale about how we found out about that. Simon Newcombe said in 1888, we're probably nearing the limit of all we can know about astronomy. He was completely wrong. Why did he say that? Because stars are so far away, no matter how big you telescope, you can't really make out anything about them except that they're just a dot of light. And so there was really no way of telling anything more. That's what he thought. But of course, humans being humans, they came up with a new amazing way to understand what's going on in the sky. The reason Simon Newcombe was wrong was that scientists had begun to understand light better. They had discovered spectroscopy, how you can break up light using a grating like that on a DVD, the lots of little stripes of data that make up the music or the video, will break light up into colors. As you can see from this. And when somebody had the bright idea to try that with star light, they discovered something quite amazing. You see, scientists have worked out that when gases glow, specific elements gave out their own combination of light waves. Very specific. So, for example, hydrogen might give out a red and a green and a blue. Different frequencies, but always in the same combination. Helium, it's a little bit more complicated, so you might get something that sounds like this. Or sodium. Now it's got these, what's called the D lines, these two yellow lines. So that maybe that was a kind of like a major seventh chord. So you could distinctly tell which element was in a star if you broke up the star light using a prism or a grating. But what really surprised people was when they discovered that the chords in distant galaxies had been stretched. So it was distinctly a hydrogen chord, but it was just a bit lower than they expected. Clearly hydrogen because, you know, it's that chord, it's not a helium or a sodium. So what was going on? Why were these spectra all stretched out and appearing in the wrong place? Here's a clue. You may have studied that light is a wave, and sound is also a wave. You may be familiar with something known as the Doppler effect. And you're probably familiar with it from sound, from the sound of cars going past. Have a listen to this. That's a bit irritating. You would have noticed as the source of the sound moved, then this pitch changed as it was coming towards you. The waves got closer together, went to a higher pitch, higher frequency, blue shifting. As it went away from you, it's called red shifting, the waves get stretched out to longer wavelengths. So how does that relate to the light from the stars, from the distant galaxies?