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YOUNG SCIENCE COMMUNICATOR’S COMPETITION THE GREAT DEBATE This radio show is dedicated to Christina Scott, whose support for astronomers was unwavering. [This is a highly dramatised version of the Great Debate, held in 1920. Many details have been neglected for brevity and clarity. Directions for the voice actors are shown with square brackets. If possible, sound effects of a crowd cheering and shouting (as directed) should be included. The voice of the narrator (which should preferably be female for some contrast) must sound older at the beginning and the end and a youthful voice in between, as directed. The voice of Shapley should be a young, enthusiastic man whereas Curtis should sound older and more distinguished.] NARRATOR [old voice]: The year was 1920, the place: the Smithsonian, Washington, the question: what is the size of the Universe? Two scientists, Harlow Shapley and Heber Curtis, met to answer this immense question once and for all in what has become known as “the Great Debate”, for which I was chairman. Ah, I remember it like it was yesterday... [Sounds of a crowd cheering] NARRATOR [younger now]: Welcome ladies and gentlemen to today's debate. We will begin with Shapley's view of the Milky Way. SHAPLEY: Well, we all know that the familiar band of stars across the sky which we call the Milky Way is in fact a disk shaped galaxy, filled with millions of stars, of which our sun is one. I propose that the Milky Way is ten times larger than previously thought [gasp from the audience] and as such, must make up the entirety of the Universe. NARRATOR: Ten times larger? A controversial view! Curtis, what is your response? CURTIS: I disagree of course! When we look out at the sky with our telescopes, we also observe beautiful, spiral, cloud-like objects, the spiral nebulae. I have seen dark patches in these nebulae similar to the dust lanes we observe in our own galaxy. I propose the spiral nebulae are island universes, galaxies like our own, filled with stars! SHAPLEY: That's absurd! By measuring the faintness of stars, I have determined the Milky Way to be 300 000 light years acrossNARRATOR: [Interrupting] May I remind the audience that a light year is a distance measure astronomers use, being the distance light travels in one year. One light year is ten trillion kilometres, making 300 000 light years an enormous distance! If Shapley's estimate is right, well... Think of it like this, if the sun was the size of an atom, the galaxy would be the size of a baseball field! SHAPLEY: Yes, and if Curtis' “island universes” [said with a sneer] are all galaxies like the Milky Way, they'd have to be millions of light years away, an unimaginable distance! CURTIS: Perhaps we should not limit our imaginations... SHAPLEY: Well... [pauses, searching for an argument] What about the flashes of light we observe in the nebulae? These novae outshine the entire nebulae for a few days. If the nebulae are truly outside our galaxy, these novae would have to output enormous amounts of energy! CURTIS: Aha! The novae are very interesting! Why do you suppose we see so many more of these novae in the spiral nebulae than amongst the stars in our galaxies if the nebulae are not themselves galaxies? [One can hear the smirk in his voice] NARRATOR: [Old voice again] Of course, we know now that those bright lights we then called novae were in fact supernovae, explosions of massive stars. These are the most powerful events in the Universe. For a few days, a supernova, the death of just one star, temporarily outshines an entire galaxy of billions of stars! Of course, Shapley didn't know that back then... SHAPLEY: They simply cannot give off so much energy! [Pauses] And I have heard you propose the sun is near the centre of the galaxy? CURTIS: [Indignant] Yes, since I see stars all around us. SHAPLEY: Ha! That's an antiquated view! Why should we be in a special place? [Scoffing] You may as well believe the Earth is flat and at the centre of the Universe! [At this, Curtis and Shapley yell incomprehensibly at each other and the crowd begins shouting as well] [The narrator is heard trying to shout the crowd into silence, eventually succeeding] NARRATOR: Ladies and gentlemen! I've just received a telegram! Will you please listen! These are Edwin Hubble's latest results. He says he measured the distance to Andromeda, the closest spiral nebula to us, and it is, beyond any doubt, outside of our own galaxy! [Shouts and cheers are heard from the crowd] CURTIS: [Smugly] Just as I said! So ShapleyNARRATOR: [Interrupting] Wait a minute! Hubble also measured distances within our own galaxy, and it seems that Shapley was right, the galaxy is indeed much bigger than expected and in fact, the sun is not at the centre of the galaxy, we seem to live quite far from it. [There is a stunned silence] SHAPLEY: So it seems we were both right. CURTIS: And both wrong. [The crowd cheers and sound fades] NARRATOR: [Old voice again] After that, Shapley and Curtis shook hands. None of us knew at the time the impact the Great Debate would have, it was one of the great moments in the story of finding our place in the Universe. As a civilization, we've gone from believing the Earth was at the centre of a very small universe, to understanding that we live on one planet of several, orbiting one star of a hundred billion, in the far corner of one galaxy amongst billions of others in a Universe bigger than anyone could have imagined!