The appearance of the aurora borealis has entranced and intrigued people from cultures across the world, inspiring art, music and stories, including tonight's Proms world premiere of Iain Bell's Aurora. But what creates it? Why is it green? Physicists Melanie Windridge, author of Aurora: In Search of the Northern Lights, and Nathan Case of Aurorawatch UK discuss the science that lies behind the Northern Lights. BBC Radio 3 New Generation Thinker Eleanor Rosamund Barraclough is the author of Beyond the Northlands: Viking Voyages and the Old Norse Sagas.