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