1 00:00:01,000 --> 00:00:05,013 Since its launch in 1990, 2 00:00:05,013 --> 00:00:08,798 Hubble has revolutionised many areas of astronomy. 3 00:00:09,300 --> 00:00:12,862 From imaging the most stunning phenomena in the cosmos, 4 00:00:12,862 --> 00:00:16,484 to studying invisible parts of the Universe, 5 00:00:16,484 --> 00:00:20,800 to observing the most distant objects ever seen. 6 00:00:21,000 --> 00:00:23,427 This is the first part of an exploration 7 00:00:23,427 --> 00:00:26,237 of some of Hubble’s most important discoveries 8 00:00:26,237 --> 00:00:29,800 in its almost 27-year history. 9 00:00:35,100 --> 00:00:39,600 Hubble’s biggest discoveries - part I 10 00:00:43,000 --> 00:00:45,500 Even before its launch, 11 00:00:45,500 --> 00:00:50,677 astronomers had already defined several important scientific goals for Hubble. 12 00:00:50,677 --> 00:00:53,371 Among them was the detailed study 13 00:00:53,371 --> 00:00:57,212 of the formation and evolution of galaxies. 14 00:00:58,100 --> 00:01:00,486 In 1995, 15 00:01:00,486 --> 00:01:06,570 Hubble spent ten days observing a tiny patch of dark sky. 16 00:01:06,570 --> 00:01:10,656 However, when this image came back 17 00:01:10,656 --> 00:01:13,512 — the famous Hubble Deep Field — 18 00:01:13,512 --> 00:01:16,902 it was not so dark after all. 19 00:01:19,200 --> 00:01:21,400 In an area of sky with a width equal 20 00:01:21,400 --> 00:01:23,404 to just one twelfth that of the full Moon, 21 00:01:23,404 --> 00:01:27,003 Hubble had found almost 3 000 distant galaxies. 22 00:01:27,003 --> 00:01:28,977 Some of them existed 23 00:01:28,977 --> 00:01:32,274 only two billion years after the Big Bang. 24 00:01:32,274 --> 00:01:36,300 Their diminutive size and irregular structure 25 00:01:36,300 --> 00:01:39,000 strongly indicated that today’s galaxies 26 00:01:39,000 --> 00:01:42,700 formed after smaller ones merged. 27 00:01:45,000 --> 00:01:47,321 The survey was so successful 28 00:01:47,321 --> 00:01:51,105 that it was followed by the Hubble Ultra-Deep Field in 2004 29 00:01:55,100 --> 00:01:58,400 and the eXtreme-Deep Field in 2012. 30 00:02:02,000 --> 00:02:06,941 However, the Deep Fields were far from being the only programmes 31 00:02:06,941 --> 00:02:10,517 to study the distant Universe. 32 00:02:10,517 --> 00:02:11,400 In recent years, 33 00:02:11,400 --> 00:02:16,555 the Frontier Fields have used clusters of galaxies 34 00:02:16,555 --> 00:02:18,877 as magnifying lenses 35 00:02:18,877 --> 00:02:24,356 to study objects that are otherwise too faint to be seen by Hubble. 36 00:02:27,000 --> 00:02:28,800 In another survey, 37 00:02:28,800 --> 00:02:32,437 the most distant known object was discovered: 38 00:02:32,437 --> 00:02:39,000 this remote galaxy existed just 400 million years after the Big Bang. 39 00:02:40,500 --> 00:02:42,000 In 2016, 40 00:02:42,000 --> 00:02:44,744 these deep images also helped 41 00:02:44,744 --> 00:02:49,805 to count the total number of galaxies in the observable Universe: 42 00:02:49,805 --> 00:02:52,290 two trillion. 43 00:02:54,000 --> 00:02:56,098 Another scientific goal of Hubble 44 00:02:56,098 --> 00:02:59,628 was to determine the Hubble constant. 45 00:02:59,628 --> 00:03:02,200 This constant is a measurement 46 00:03:02,200 --> 00:03:05,154 of how fast the Universe is currently expanding 47 00:03:05,154 --> 00:03:09,055 — as discovered by the astronomer Edwin Hubble. 48 00:03:13,600 --> 00:03:13,722 As such, 49 00:03:13,722 --> 00:03:18,296 the Hubble constant is a key value needed to understand the cosmos. 50 00:03:23,173 --> 00:03:24,800 Before Hubble’s launch, 51 00:03:24,800 --> 00:03:28,281 estimates of the value of the constant differed by a factor of two. 52 00:03:31,000 --> 00:03:31,400 With the help of the telescope, 53 00:03:31,400 --> 00:03:36,245 astronomers were able to determine its value to a higher precision. 54 00:03:42,000 --> 00:03:43,002 Even today, 55 00:03:43,002 --> 00:03:46,450 Hubble continues to measure this constant 56 00:03:46,450 --> 00:03:47,948 using different methods. 57 00:03:47,950 --> 00:03:50,433 However, the latest results indicate that 58 00:03:50,433 --> 00:03:56,261 the Hubble constant is different for the local and the primordial Universe. 59 00:03:56,261 --> 00:03:59,600 This hints at a problem 60 00:03:59,600 --> 00:04:02,275 at the very core of our understanding of the cosmos. 61 00:04:04,000 --> 00:04:07,755 With the precise measurements of the Hubble constant, 62 00:04:07,756 --> 00:04:10,913 the Hubble telescope was also able to determine 63 00:04:10,913 --> 00:04:12,585 the age of the Universe. 64 00:04:15,300 --> 00:04:16,927 Before its launch, 65 00:04:16,927 --> 00:04:18,831 estimates for the Universe’s age 66 00:04:18,831 --> 00:04:20,642 ranged from 10 to 20 billion years. 67 00:04:20,642 --> 00:04:24,752 Now we are able to determine the age of the Universe 68 00:04:24,752 --> 00:04:27,120 to within a few million years. 69 00:04:29,000 --> 00:04:32,298 Hubble observed stars with variable brightness 70 00:04:32,298 --> 00:04:34,086 — known as Cepheids — 71 00:04:34,086 --> 00:04:36,083 in distant galaxies. 72 00:04:36,083 --> 00:04:38,568 By doing so, astronomers were able 73 00:04:38,568 --> 00:04:40,983 to accurately determine the scale 74 00:04:40,983 --> 00:04:43,653 and age of the observable Universe. 75 00:04:47,300 --> 00:04:49,853 Hubble also played a critical role 76 00:04:49,853 --> 00:04:53,521 in one of the most groundbreaking discoveries of the 20th century: 77 00:04:53,521 --> 00:04:57,237 the accelerating expansion of the Universe. 78 00:04:57,237 --> 00:05:01,114 It imaged distant supernova explosions, 79 00:05:01,114 --> 00:05:03,970 and by measuring how bright these explosions appeared to be, 80 00:05:03,970 --> 00:05:10,426 the distances to their host galaxies could be calculated. 81 00:05:10,427 --> 00:05:13,212 Hubble's accurate measurements, 82 00:05:13,212 --> 00:05:15,139 not possible from the ground, 83 00:05:15,139 --> 00:05:17,554 were crucial in showing that 84 00:05:17,554 --> 00:05:21,989 these supernovae were fainter than expected, 85 00:05:21,989 --> 00:05:26,865 and so the Universe's expansion must be speeding up. 86 00:05:28,000 --> 00:05:30,116 Astronomers now believe 87 00:05:30,116 --> 00:05:34,876 this expansion is driven by a mysterious dark energy. 88 00:05:34,950 --> 00:05:39,056 With its sharp eye and precise measurements 89 00:05:39,056 --> 00:05:44,373 — made outside Earth’s disruptive atmosphere — 90 00:05:44,373 --> 00:05:47,601 Hubble has revolutionised our knowledge 91 00:05:47,601 --> 00:05:51,432 of cosmology and the evolution of the Universe. 92 00:05:52,600 --> 00:05:57,260 But these are far from the only important discoveries made by Hubble 93 00:05:57,260 --> 00:06:01,997 — more will be revealed in the second part of this double video.