1 00:00:18,000 --> 00:00:19,000 This is the Hubblecast! 2 00:00:19,000 --> 00:00:23,000 News and images from the NASA/ESA Hubble Space Telescope. 3 00:00:23,000 --> 00:00:28,000 Travelling through time and space with our host Doctor J a.k.a. Dr. Joe Liske. 4 00:00:28,000 --> 00:00:36,000 Hello, and welcome to this fourth, special episode of the Hubblecast, celebrating the International Year of Astronomy in 2009. 5 00:00:36,000 --> 00:00:42,000 In the last episode, we saw how the advance of technology through the 1970s and ‘80s, revolutionised astronomy. 6 00:00:42,000 --> 00:00:50,000 Today, we’ll discuss how astronomers detected and measured light over the years, from hand-drawings to electronic detectors. 7 00:00:53,000 --> 00:00:59,000 400 years ago, when Galileo Galilei wanted to show others what he saw through his telescope, he had to make drawings. 8 00:00:59,000 --> 00:01:02,000 The pockmarked face of the Moon. 9 00:01:02,000 --> 00:01:05,000 The dance of the Jovian satellites. 10 00:01:07,000 --> 00:01:08,000 Sunspots. 11 00:01:09,000 --> 00:01:11,000 Or the stars in Orion. 12 00:01:11,000 --> 00:01:15,000 He took his drawings and published them in a small book, The Starry Messenger. 13 00:01:15,000 --> 00:01:19,000 That was the only way he could share his discoveries with others. 14 00:01:19,000 --> 00:01:23,000 For well over two centuries, astronomers also had to be artists. 15 00:01:23,000 --> 00:01:27,000 Peering through their eyepieces, they made detailed drawings of what they saw. 16 00:01:27,000 --> 00:01:30,000 The stark landscape of the Moon. 17 00:01:30,000 --> 00:01:33,000 A storm in the atmosphere of Jupiter. 18 00:01:33,000 --> 00:01:35,000 The subtle veil of gas in a distant nebula. 19 00:01:35,000 --> 00:01:39,000 And sometimes they over-interpreted what they saw. 20 00:01:39,000 --> 00:01:46,000 Dark linear features on the surface of Mars were thought to be canals suggesting civilised life on the surface of the red planet. 21 00:01:46,000 --> 00:01:50,000 We now know that the canals were an optical illusion. 22 00:01:50,000 --> 00:02:01,000 What astronomers really needed was an objective way to record the light collected by the telescopes without the information first having to pass through their brains and their drawing pens. 23 00:02:01,000 --> 00:02:04,000 Photography came to the rescue. 24 00:02:06,000 --> 00:02:07,000 The first daguerreotype of the Moon. 25 00:02:07,000 --> 00:02:10,000 It was made in 1840 by Henry Draper. 26 00:02:10,000 --> 00:02:17,000 Photography was less than 15 years old, but astronomers had already seized on its revolutionary possibilities. 27 00:02:17,000 --> 00:02:20,000 So how did photography work? 28 00:02:20,000 --> 00:02:26,000 Well the sensitive emulsion of a photographic plate contained small grains of silver halide. 29 00:02:26,000 --> 00:02:29,000 Expose them to light, and they turn dark. 30 00:02:29,000 --> 00:02:35,000 So the result was a negative image of the sky, with dark stars on a light background. 31 00:02:35,000 --> 00:02:40,000 But the real bonus was that a photographic plate can be exposed for hours on end. 32 00:02:40,000 --> 00:02:45,000 When you take in the night sky with your own eyes, once they‘re dark adapted, 33 00:02:45,000 --> 00:02:49,000 you don’t see more and more stars just by looking longer. 34 00:02:49,000 --> 00:02:52,000 But with a photographic plate you can do just that. 35 00:02:52,000 --> 00:02:55,000 You can collect and add up the light over hours on end. 36 00:02:55,000 --> 00:02:59,000 So a longer exposure reveals more and more stars. 37 00:02:59,000 --> 00:03:04,000 And more. And more. And then some. 38 00:03:05,000 --> 00:03:11,000 In the 1950s, the Schmidt telescope at the Palomar Observatory was used to photograph the entire northern sky. 39 00:03:11,000 --> 00:03:16,000 Almost 2000 photographic plates, each exposed for nearly an hour. 40 00:03:16,000 --> 00:03:19,000 A treasure trove of discovery. 41 00:03:19,000 --> 00:03:23,000 Photography had turned observational astronomy into a true science. 42 00:03:23,000 --> 00:03:28,000 Objective, measurable, and reproducible. 43 00:03:28,000 --> 00:03:32,000 But silver was slow. You had to be patient. 44 00:03:34,000 --> 00:03:36,000 The digital revolution changed all that. 45 00:03:36,000 --> 00:03:41,000 Silicon replaced silver. Pixels replaced grains. 46 00:03:43,000 --> 00:03:46,000 Even in consumer cameras, we no longer use photographic film. 47 00:03:46,000 --> 00:03:54,000 Instead, images are recorded on a light-sensitive chip: a charge coupled device, or CCD for short. 48 00:03:54,000 --> 00:03:58,000 Professional CCDs are extremely efficient. 49 00:03:58,000 --> 00:04:05,000 And to make them even more sensitive, they are cooled down to well below freezing, using liquid nitrogen. 50 00:04:05,000 --> 00:04:11,000 Almost every photon is registered. As a result, exposure times can be much shorter. 51 00:04:12,000 --> 00:04:19,000 What the Palomar Observatory Sky Survey achieved in an hour, a CCD can now do in a few short minutes. 52 00:04:19,000 --> 00:04:22,000 Using a smaller telescope. 53 00:04:22,000 --> 00:04:25,000 The silicon revolution is far from over. 54 00:04:25,000 --> 00:04:30,000 Astronomers have built huge CCD cameras with hundreds of millions of pixels. 55 00:04:30,000 --> 00:04:33,000 And there’s more to come. 56 00:04:35,000 --> 00:04:39,000 The big advantage of digital images is that they’re, well, digital. 57 00:04:39,000 --> 00:04:42,000 They’re all set and ready to be worked on with computers. 58 00:04:42,000 --> 00:04:47,000 Astronomers use specialised software to process their observations of the sky. 59 00:04:47,000 --> 00:04:54,000 Stretching, or contrast enhancing, reveals the faintest features of nebulae or galaxies. 60 00:04:54,000 --> 00:05:00,000 Colour coding enhances and brings out the structures that would otherwise be difficult to see. 61 00:05:00,000 --> 00:05:06,000 Moreover, by combining multiple images of the same object that were taken through different colour filters, 62 00:05:06,000 --> 00:05:13,000 one can produce spectacular composites that blur the boundary between science and art. 63 00:05:13,000 --> 00:05:16,000 You too can benefit from digital astronomy. 64 00:05:16,000 --> 00:05:22,000 It has never been so easy to dig up and enjoy the amazing images of the cosmos. 65 00:05:22,000 --> 00:05:26,000 Pictures of the Universe are always just a mouse click away! 66 00:05:27,000 --> 00:05:34,000 Robotic telescopes, equipped with sensitive electronic detectors are keeping watch over the sky, right now. 67 00:05:35,000 --> 00:05:41,000 The Sloan telescope in New Mexico has photographed and catalogued over a hundred million celestial objects, 68 00:05:41,000 --> 00:05:48,000 measured distances to a million galaxies, and discovered a hundred thousand new quasars. 69 00:05:48,000 --> 00:05:54,000 But one survey is not enough. The Universe is an ever-changing place. 70 00:05:54,000 --> 00:05:59,000 Icy comets come and go, leaving scattered debris in their wake. 71 00:06:01,000 --> 00:06:03,000 Asteroids zip by. 72 00:06:03,000 --> 00:06:10,000 Distant planets orbit their mother stars, temporarily blocking part of the star’s light. 73 00:06:10,000 --> 00:06:14,000 Supernovas explode, while elsewhere new stars are born. 74 00:06:16,000 --> 00:06:23,000 Pulsars flash, gamma-ray bursts detonate, black holes accrete. 75 00:06:25,000 --> 00:06:32,000 To keep track of these grand plays of Nature, astronomers want to carry out all-sky surveys every year. 76 00:06:32,000 --> 00:06:35,000 Or every month. Or twice a week. 77 00:06:35,000 --> 00:06:40,000 At least that’s the ambitious goal of the Large Synoptic Survey Telescope. 78 00:06:40,000 --> 00:06:49,000 If completed in 2015, its three-gigapixel camera will open up a webcam window on the Universe. 79 00:06:49,000 --> 00:06:57,000 More than fulfilling astronomers’ dreams, this reflecting telescope will photograph almost the entire sky every three nights. 80 00:07:01,000 --> 00:07:04,000 Thank you for joining me in this fourth episode of the special series. 81 00:07:04,000 --> 00:07:10,000 Next time, we’ll see how telescopes can study the Universe we can’t see with our own eyes. 82 00:07:10,000 --> 00:07:13,000 This is Dr. J, signing off for the HubbleCast. 83 00:07:13,000 --> 00:07:17,000 Once again, nature has surprised us beyond our wildest imagination.