1 00:00:17,795 --> 00:00:19,644 This is the Hubblecast. 2 00:00:19,645 --> 00:00:23,229 News and images from the NASA / ESA Hubble Space Telescope. 3 00:00:23,275 --> 00:00:26,823 Travelling through time and space with our host, Dr. J 4 00:00:26,855 --> 00:00:29,228 EPISODE 21: From silver to silicon a.k.a. Dr. Joe Liske. 5 00:00:29,263 --> 00:00:32,365 Hello and welcome to this fourth special episode of the Hubblecast 6 00:00:32,366 --> 00:00:35,916 celebrating the International Year of Astronomy in 2009. 7 00:00:36,432 --> 00:00:39,396 In the last episode we saw how the advance of technology 8 00:00:39,426 --> 00:00:43,029 through the 1970s and 80s revolutionised astronomy. 9 00:00:43,343 --> 00:00:47,628 Today we'll discuss how astronomers detected and measured light over the years. 10 00:00:47,629 --> 00:00:50,280 From hand drawings to electronic detectors. 11 00:00:52,451 --> 00:00:55,955 400 years ago, when Galileo Galilei wanted to show others 12 00:00:55,982 --> 00:00:59,369 what he saw through his telescope, he had to make drawings. 13 00:01:00,082 --> 00:01:02,569 The pockmarked face of the Moon. 14 00:01:03,116 --> 00:01:05,977 The dance of the Jovian satellites. 15 00:01:07,409 --> 00:01:09,101 Sunspots. 16 00:01:09,183 --> 00:01:10,907 Or the stars in Orion. 17 00:01:10,942 --> 00:01:15,728 He took his drawings and published them in a small book, The Starry Messenger. 18 00:01:15,729 --> 00:01:18,856 That was the only way he could share his discoveries with others. 19 00:01:19,469 --> 00:01:23,395 For well over two centuries astronomers also have to be artists. 20 00:01:23,520 --> 00:01:27,656 Peering through their eye pieces, they made detailed drawings of what they saw. 21 00:01:28,226 --> 00:01:30,071 The stark landscape of the Moon. 22 00:01:30,379 --> 00:01:33,029 A storm in the atmosphere of Jupiter. 23 00:01:33,030 --> 00:01:35,979 The subtle veil of gas in a distant nebulae. 24 00:01:35,980 --> 00:01:39,517 And sometimes they over-interpreted what they saw. 25 00:01:39,518 --> 00:01:43,610 Dark linear features on the surface of Mars were thought to be canals 26 00:01:43,611 --> 00:01:47,000 suggesting civilised life on the surface of the red planet. 27 00:01:47,001 --> 00:01:50,192 We now know that the canals were an optical illusion. 28 00:01:50,921 --> 00:01:54,218 What astronomers really needed was an objective way to record 29 00:01:54,253 --> 00:01:58,909 the light collected by the telescopes without the information first having to pass 30 00:01:58,944 --> 00:02:01,586 through their brains and their drawing pens. 31 00:02:01,587 --> 00:02:04,074 Photography came to the rescue. 32 00:02:05,430 --> 00:02:08,099 The first daguerreotype of the Moon. 33 00:02:08,100 --> 00:02:11,018 It was made in 1840 by Henry Draper. 34 00:02:11,019 --> 00:02:13,345 Photography was less than 15 years old, 35 00:02:13,346 --> 00:02:17,474 but astronomers had already seized on their revolutionary possibilities. 36 00:02:17,979 --> 00:02:20,318 So haw did photography work? 37 00:02:20,353 --> 00:02:23,397 Well, the sensitive emulsion of a photographic plate 38 00:02:23,432 --> 00:02:26,368 contained small grains of silver halide. 39 00:02:26,369 --> 00:02:29,072 Expose them to light, and they turn dark. 40 00:02:29,073 --> 00:02:31,696 So, the result was a negative image of the sky, 41 00:02:31,731 --> 00:02:35,006 with dark stars on a light background. 42 00:02:35,226 --> 00:02:41,022 But the real bonus was that the photographic plate can be exposed for hours on end. 43 00:02:41,057 --> 00:02:43,605 When you take in the night skies with your own eyes, 44 00:02:43,606 --> 00:02:49,095 once they're dark adapted, you don't see more and more stars just by looking longer. 45 00:02:49,470 --> 00:02:52,203 But with a photographic plate you can do just that. 46 00:02:52,266 --> 00:02:55,744 You can collect and add up the light over hours on end. 47 00:02:55,745 --> 00:03:00,007 So, a longer exposure reveals more and more stars. 48 00:03:00,008 --> 00:03:03,865 And more. And more. And then some. 49 00:03:05,059 --> 00:03:08,949 In the 1950s, the Schmidt Telescope at the Palomar Observatory 50 00:03:08,984 --> 00:03:11,909 was used to photograph the entire northern sky. 51 00:03:12,248 --> 00:03:16,861 Almost 2,000 photographic plates, each exposed for nearly an hour. 52 00:03:16,862 --> 00:03:19,472 A treasure trove of discovery. 53 00:03:19,964 --> 00:03:23,879 Photography had turned observational astronomy into a true science. 54 00:03:23,880 --> 00:03:28,371 Objective, measurable and reproducible. 55 00:03:28,372 --> 00:03:32,409 But silver was slow. You had to be patient. 56 00:03:34,226 --> 00:03:36,875 The digital revolution changed all that. 57 00:03:36,876 --> 00:03:40,776 Silicon replaced silver, pixels replaced grains. 58 00:03:43,438 --> 00:03:47,122 Even in consumer cameras, we no longer use photographic film. 59 00:03:47,123 --> 00:03:50,597 Instead, images are recorded on a light sensitive chip: 60 00:03:50,598 --> 00:03:54,782 a charged coupled device or CCD for short. 61 00:03:54,783 --> 00:03:58,496 Professional CCDs are extremely efficient. 62 00:03:58,497 --> 00:04:00,611 And to make them even more sensitive 63 00:04:00,651 --> 00:04:04,885 they are cooled down to well below freezing using liquid nitrogen. 64 00:04:05,264 --> 00:04:07,826 Almost every photon is registered. 65 00:04:07,827 --> 00:04:10,900 As a result, exposure times can be much shorter. 66 00:04:12,707 --> 00:04:16,414 What the Palomar Observatory Sky Survey achieved in an hour, 67 00:04:16,449 --> 00:04:20,085 a CCD can now do in a few short minutes. 68 00:04:20,086 --> 00:04:22,658 Using a smaller telescope. 69 00:04:22,659 --> 00:04:25,118 The silicon revolution is far from over. 70 00:04:25,119 --> 00:04:30,714 Astronomers have built huge CCD cameras with hundreds of millions of pixels. 71 00:04:30,715 --> 00:04:33,598 And there's more to come. 72 00:04:34,936 --> 00:04:39,567 The big advantage of digital images is that they're... well, digital. 73 00:04:39,568 --> 00:04:42,772 They're all set and ready to be worked on with computers. 74 00:04:42,773 --> 00:04:47,788 Astronomers use specialised software to process their observations of the sky. 75 00:04:47,823 --> 00:04:50,713 Stretching, or contrast enhancing, 76 00:04:50,748 --> 00:04:54,053 reveals the faintest features of nebulae or galaxies. 77 00:04:54,396 --> 00:04:57,545 Colour coding enhances and brings out 78 00:04:57,580 --> 00:05:00,326 the structures that would otherwise be difficult to see. 79 00:05:00,327 --> 00:05:04,695 Moreover, by combining multiple images of the same object, 80 00:05:04,730 --> 00:05:07,245 that were taken through different colour filters, 81 00:05:07,280 --> 00:05:11,380 one can produce spectacular composites that blur the boundary 82 00:05:11,415 --> 00:05:13,303 between science and art. 83 00:05:13,304 --> 00:05:16,794 You too can benefit from digital astronomy. 84 00:05:16,829 --> 00:05:22,755 It has never been so easy to dig up and enjoy the amazing images of the cosmos. 85 00:05:22,790 --> 00:05:26,714 Pictures of the Universe are always just a mouse click away! 86 00:05:27,707 --> 00:05:31,112 Robotic telescopes, equipped with sensitive electronic detectors 87 00:05:31,147 --> 00:05:34,223 are keeping watch over the sky, right now. 88 00:05:34,740 --> 00:05:37,113 The Sloan Telescope in New Mexico 89 00:05:37,148 --> 00:05:41,017 has photographed and catalogued over a hundred million celestial objects, 90 00:05:41,052 --> 00:05:43,985 measured distances to a million galaxies 91 00:05:44,020 --> 00:05:48,170 and discovered a hundred thousand new quasars. 92 00:05:48,662 --> 00:05:51,291 But one survey is not enough. 93 00:05:51,292 --> 00:05:54,150 The Universe is an ever-changing place. 94 00:05:54,764 --> 00:05:59,657 Icy comets come and go, leaving scattered debris in their wake. 95 00:06:00,887 --> 00:06:03,110 Asteroids zip by. 96 00:06:03,946 --> 00:06:09,818 Distant planets orbit their mother stars, temporarily blocking part of the star's light. 97 00:06:09,819 --> 00:06:14,641 Supernovas explode, while elsewhere new stars are born. 98 00:06:15,808 --> 00:06:19,972 Pulsars flash, gamma-ray burst detonate, 99 00:06:20,852 --> 00:06:25,030 black holes accrete. 100 00:06:25,041 --> 00:06:28,073 To keep track of these grand plays of Nature, 101 00:06:28,108 --> 00:06:32,219 astronomers want to carry out all-sky surveys every year. 102 00:06:32,220 --> 00:06:33,952 Or every month. 103 00:06:33,987 --> 00:06:35,684 Or twice a week. 104 00:06:35,863 --> 00:06:41,187 At least that's the ambitious goal of the Large Synoptic Survey Telescope. 105 00:06:41,222 --> 00:06:45,750 If completed in 2015, its three-gigapixel camera 106 00:06:45,751 --> 00:06:49,180 will open up a webcam window on the Universe. 107 00:06:49,215 --> 00:06:53,014 More than fulfilling astronomers' dreams, this reflecting telescope 108 00:06:53,049 --> 00:06:58,043 will photograph almost the entire sky every three nights. 109 00:07:01,275 --> 00:07:04,853 Thank you for joining me in this fourth episode of the special series. 110 00:07:04,854 --> 00:07:08,058 Next time we will see how telescopes can study the Universe 111 00:07:08,059 --> 00:07:10,541 that we can't see with our own eyes. 112 00:07:11,036 --> 00:07:13,729 This is Dr. J signing off for the Hubblecast. 113 00:07:13,730 --> 00:07:17,885 Once again, nature has surprised us beyond our wildest imagination... 114 00:07:18,914 --> 00:07:20,914 Hubblecast is produced by ESA / Hubble 115 00:07:20,915 --> 00:07:22,915 at the European Southern Observatory in Germany. 116 00:07:24,067 --> 00:07:26,067 The Hubble mission is a project of international cooperation 117 00:07:26,068 --> 00:07:28,068 between NASA and the European Space Agency.