 G'day, I'm Phil Dooley. I'm a science communicator at the Research School of Physics at ANU 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 your 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 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 starlight they discovered something quite amazing You see scientists have worked out that when gases glowed 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 look 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 starlight 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?