2. Bigger is better 00:00:19:20 00:00:22:06 At night, your eyes adapt to the dark. 00:00:22:07 00:00:26:10 Your pupils widen to let more light into your eyes. 00:00:26:11 00:00:31:16 As a result, you can see dimmer objects, and fainter stars. 00:00:31:17 00:00:35:12 Now imagine you had pupils one metre across. 00:00:35:13 00:00:39:18 You'd look pretty strange but you'd also have supernatural eyesight! 00:00:39:19 00:00:43:05 And that's what telescopes do for you. 00:00:45:16 00:00:48:10 A telescope is like a funnel. 00:00:48:11 00:00:54:00 Its main lens or mirror collects the starlight and brings it all together into your eye. 00:00:56:20 00:01:01:14 The bigger the lens or the mirror of a telescope, the fainter the objects you can see. 00:01:01:05 00:01:04:12 So size really is everything. 00:01:04:13 00:01:07:04 But how big can you make a telescope? 00:01:07:05 00:01:10:05 Well, actually not too big if it's a refractor. 00:01:13:05 00:01:16:12 The starlight has to pass through the main lens. 00:01:16:13 00:01:19:21 And so you can only support it around its edge. 00:01:19:22 00:01:25:17 Now if you make the lens too big it becomes too heavy, and it starts deforming under its own weight. 00:01:25:18 00:01:29:10 That means that the image will be distorted. 00:01:31:03 00:01:38:03 The largest refractor in history was completed in 1897, at Yerkes Observatory outside Chicago. 00:01:38:04 00:01:41:07 Its main lens was just over one metre across. 00:01:41:08 00:01:45:22 But its tube was an incredible 18 metres long. 00:01:45:23 00:01:52:12 With the completion of the Yerkes telescope, the builders of refracting telescopes had pretty much reached their limit. 00:01:52:13 00:01:54:16 You want bigger telescopes? 00:01:54:17 00:01:56:15 Think mirrors. 00:02:00:20 00:02:06:21 In a reflecting telescope, the starlight bounces off a mirror instead of passing through a lens. 00:02:06:22 00:02:13:05 That means that you can make the mirror a lot thinner than a lens, and you can support it from the back. 00:02:13:06 00:02:18:10 The result is that you can build a lot larger mirrors than lenses. 00:02:19:09 00:02:23:12 Big mirrors came to southern California a century ago. 00:02:23:13 00:02:28:17 Back then, Mount Wilson was a remote peak in the wilderness of the San Gabriel mountains. 00:02:28:18 00:02:32:22 The sky was clear and the nights were dark. 00:02:32:23 00:02:37:11 Here, George Ellery Hale first built a 1.5 metre telescope. 00:02:37:12 00:02:42:04 Smaller than Lord Rosse's retired Leviathan, it was of much better quality. 00:02:42:05 00:02:45:24 And at a much better site, too. 00:02:46:00 00:02:51:11 Hale talked local businessman John Hooker into financing a 2.5 metre instrument. 00:02:51:12 00:02:56:08 Tonnes of glass and riveted steel were hauled up Mount Wilson. 00:02:56:09 00:02:59:20 The Hooker telescope was completed in 1917. 00:02:59:21 00:03:04:01 It would remain the largest telescope in the world for 30 years. 00:03:04:02 00:03:09:05 A big piece of cosmic artillery, ready to attack the Universe. 00:03:12:06 00:03:14:22 And attack it did. 00:03:14:23 00:03:18:00 Along with the incredible size of the new telescope came... 00:03:18:01 00:03:21:00 ...transformations in the way the image was viewed. 00:03:21:01 00:03:24:14 Astronomers no longer peered through the eyepiece of the new giant. 00:03:24:15 00:03:29:18 But instead collected the light on photographic plates for hours on end. 00:03:29:19 00:03:34:15 Never before had anyone peered so far into the cosmos. 00:03:34:16 00:03:38:23 Spiral nebulae turned out to be brimming with individual stars. 00:03:38:24 00:03:43:09 Could they be sprawling stellar systems like our own Milky Way? 00:03:43:10 00:03:47:14 In the Andromeda Nebula, Edwin Hubble discovered a particular type of star... 00:03:47:15 00:03:51:04 ...that changes its brightness with clocklike precision. 00:03:51:05 00:03:55:13 From his observations Hubble was able to deduce the distance to Andromeda: 00:03:55:14 00:03:59:19 almost a million light-years. 00:03:59:20 00:04:06:13 Spiral nebulae, like Andromeda, were clearly individual galaxies in their own right. 00:04:08:05 00:04:11:03 But that wasn't the only incredible thing. 00:04:11:04 00:04:15:20 Most of these galaxies were found to be moving away from the Milky Way. 00:04:15:21 00:04:21:10 At Mount Wilson, Hubble discovered that the nearby galaxies were receding at small velocities... 00:04:21:11 00:04:26:07 ...whereas the distant galaxies were moving away at a much faster pace. 00:04:26:08 00:04:27:13 The conclusion? 00:04:27:14 00:04:30:08 The Universe was expanding. 00:04:30:09 00:04:37:05 The Hooker telescope had given scientists the most profound astronomical discovery of the 20th century. 00:04:39:21 00:04:44:10 Thanks to the telescope, we have traced the history of the Universe. 00:04:44:11 00:04:48:17 A little less than 14 billion years ago, the Universe was born... 00:04:48:18 00:04:52:25 ...in a huge explosion of time and space, matter and energy, called... 00:04:52:25 00:04:55:09 ...the Big Bang. 00:04:55:10 00:05:01:06 Tiny quantum ripples grew into dense patches in the primordial brew. 00:05:01:07 00:05:03:24 From these, galaxies condensed. 00:05:04:00 00:05:07:15 A stunning variety of sizes and shapes. 00:05:10:08 00:05:14:05 Nuclear fusion in the cores of stars produced new atoms. 00:05:14:06 00:05:18:16 Carbon, oxygen, iron, gold. 00:05:18:17 00:05:23:10 Supernova explosions blew these heavy elements back into space. 00:05:23:11 00:05:26:22 Raw material for the formation of new stars. 00:05:26:23 00:05:28:15 And planets! 00:05:30:15 00:05:38:17 Someday, somewhere, somehow, simple organic molecules evolved into living organisms. 00:05:38:18 00:05:44:09 Life is one miracle in an ever-evolving Universe. 00:05:44:10 00:05:46:17 We are stardust. 00:05:46:18 00:05:50:20 It's a grand vision and a sweeping story. 00:05:50:21 00:05:54:24 Brought to us through telescopic observations. 00:05:55:00 00:05:59:11 Imagine: without the telescope we would know about just six planets... 00:05:59:12 00:06:01:24 ...one moon, and a few thousand stars. 00:06:02:00 00:06:06:05 Astronomy would still be in its infancy. 00:06:07:10 00:06:11:06 Like buried treasures, the outposts of the Universe have beckoned to the... 00:06:11:07 00:06:13:20 ...adventurous from immemorial times. 00:06:13:21 00:06:19:06 Princes and potentates, political or industrial, equally with men of science... 00:06:19:07 00:06:24:00 ...have felt the lure of the uncharted seas of space, and through their provision... 00:06:24:01 00:06:29:05 ...of instrumental means the sphere of exploration has rapidly widened. 00:06:43:13 00:06:46:11 George Ellery Hale had one final dream: 00:06:46:12 00:06:50:18 to build a telescope twice as large as the previous record holder. 00:06:50:19 00:06:54:17 Meet the grand old lady of 20th century astronomy. 00:06:54:18 00:06:59:17 The five metre Hale telescope at Palomar Mountain. 00:06:59:18 00:07:04:08 Over five hundred tonnes of moving weight, yet so precisely balanced... 00:07:04:09 00:07:08:11 ...that it moves as gracefully as a ballerina. 00:07:08:12 00:07:14:00 Its 40 tonne mirror reveals stars 40 million times fainter than the eye can see. 00:07:14:01 00:07:19:00 Completed in 1948, the Hale telescope gave us unsurpassed views of planets... 00:07:19:01 00:07:22:15 ...star clusters, nebulae and galaxies. 00:07:24:20 00:07:28:19 Giant Jupiter, with its many moons. 00:07:28:20 00:07:32:21 The stunning Flame Nebula. 00:07:32:22 00:07:38:00 Faint wisps of gas in the Orion Nebula. 00:07:43:15 00:07:45:22 But could we go bigger still? 00:07:45:23 00:07:50:00 Well, soviet astronomers tried in the late 1970s. 00:07:50:01 00:07:54:10 High up in the Caucasus mountains, they built the Bolshoi Teleskop Azimutalnyi... 00:07:54:11 00:07:58:17 ...sporting a primary mirror six metres in diameter. 00:07:58:18 00:08:01:10 But it never really lived up to its expectations. 00:08:01:11 00:08:05:13 It was simply too big, too expensive, and too difficult. 00:08:05:14 00:08:08:19 So did telescope builders have to give up at that point? 00:08:08:20 00:08:12:07 Did they have to bury their dreams of even bigger instruments? 00:08:12:08 00:08:15:19 Had the history of the telescope come to a premature end? 00:08:15:20 00:08:17:04 Well, of course not. 00:08:17:05 00:08:20:07 Today we have 10 metre telescopes in operation. 00:08:20:08 00:08:22:23 And even bigger ones are on the drawing board. 00:08:22:24 00:08:24:12 What was the solution? 00:08:24:13 00:08:26:10 New technologies.