1 00:00:00,800 --> 00:00:03,107 Since its launch in 1990, 2 00:00:03,107 --> 00:00:07,684 Hubble has revolutionised many areas of astronomy. 3 00:00:07,884 --> 00:00:12,940 From imaging the most stunning phenomena in the cosmos, 4 00:00:12,940 --> 00:00:15,697 to studying invisible parts of the Universe, 5 00:00:15,697 --> 00:00:19,743 to observing the most distant objects ever seen. 6 00:00:19,843 --> 00:00:23,611 This is the first part of an exploration 7 00:00:23,612 --> 00:00:27,210 of some of Hubble’s most important discoveries 8 00:00:27,211 --> 00:00:30,336 in its almost 27-year history. 9 00:00:42,568 --> 00:00:44,303 Even before its launch, 10 00:00:44,303 --> 00:00:46,561 astronomers had already defined 11 00:00:46,562 --> 00:00:49,960 several important scientific goals for Hubble. 12 00:00:49,961 --> 00:00:54,000 Among them was the detailed study of the formation 13 00:00:54,000 --> 00:00:57,102 and evolution of galaxies. 14 00:00:57,716 --> 00:01:04,980 In 1995, Hubble spent ten days observing a tiny patch of dark sky. 15 00:01:04,980 --> 00:01:06,275 However, when this image 16 00:01:06,275 --> 00:01:09,275 — the famous Hubble Deep Field — 17 00:01:09,275 --> 00:01:13,203 came back, it was not so dark after all. 18 00:01:13,903 --> 00:01:17,988 In an area of sky with a width equal to just 19 00:01:17,988 --> 00:01:20,950 one twelfth that of the full Moon, 20 00:01:20,960 --> 00:01:25,082 Hubble had found almost 3 000 distant galaxies. 21 00:01:25,082 --> 00:01:29,690 Some of them existed only two billion years after the Big Bang. 22 00:01:29,690 --> 00:01:34,607 Their diminutive size and irregular structure strongly indicated 23 00:01:34,607 --> 00:01:39,076 that today’s galaxies formed after smaller ones merged. 24 00:01:39,376 --> 00:01:42,201 The survey was so successful that 25 00:01:42,201 --> 00:01:47,350 it was followed by the Hubble Ultra-Deep Field in 2004 26 00:01:47,550 --> 00:01:53,152 and the eXtreme-Deep Field in 2012. 27 00:01:56,149 --> 00:01:59,970 However, the Deep Fields were far from being the only programmes 28 00:01:59,970 --> 00:02:02,193 to study the distant Universe. 29 00:02:02,193 --> 00:02:05,712 In recent years, the Frontier Fields have used 30 00:02:05,712 --> 00:02:10,233 clusters of galaxies as magnifying lenses to study 31 00:02:10,233 --> 00:02:14,585 objects that are otherwise too faint to be seen by Hubble. 32 00:02:21,488 --> 00:02:26,120 In another survey, the most distant known object was discovered. 33 00:02:26,662 --> 00:02:33,013 This remote galaxy existed just 400 million years after the Big Bang. 34 00:02:34,475 --> 00:02:37,837 In 2016, these deep images also 35 00:02:37,837 --> 00:02:43,479 helped to count the total number of galaxies in the observable Universe: 36 00:02:43,479 --> 00:02:45,319 two trillion. 37 00:02:48,319 --> 00:02:53,598 Another scientific goal of Hubble was to determine the Hubble constant. 38 00:02:53,598 --> 00:02:56,069 This constant is a measurement of how fast 39 00:02:56,069 --> 00:02:58,552 the Universe is currently expanding 40 00:02:58,552 --> 00:03:03,000 — as discovered by the astronomer Edwin Hubble. 41 00:03:07,002 --> 00:03:10,947 As such, the Hubble constant is a key value 42 00:03:10,948 --> 00:03:12,847 needed to understand the cosmos 43 00:03:16,585 --> 00:03:18,282 Before Hubble’s launch, 44 00:03:18,282 --> 00:03:23,006 estimates of the value of the constant differed by a factor of two. 45 00:03:24,002 --> 00:03:26,006 With the help of the telescope, 46 00:03:26,006 --> 00:03:31,350 astronomers were able to determine its value to a higher precision. 47 00:03:35,900 --> 00:03:37,047 Even today, 48 00:03:37,047 --> 00:03:41,461 Hubble continues to measure this constant using different methods. 49 00:03:41,461 --> 00:03:46,165 However, the latest results indicate that the Hubble constant is 50 00:03:46,165 --> 00:03:49,736 different for the local and the primordial Universe. 51 00:03:49,736 --> 00:03:51,838 This hints at a problem 52 00:03:51,838 --> 00:03:55,667 at the very core of our understanding of the cosmos. 53 00:03:58,162 --> 00:04:00,722 With the precise measurements of the Hubble constant, 54 00:04:00,722 --> 00:04:06,337 the Hubble telescope was also able to determine the age of the Universe. 55 00:04:08,010 --> 00:04:09,123 Before its launch, 56 00:04:09,123 --> 00:04:15,028 estimates for the Universe’s age ranged from 10 to 20 billion years. 57 00:04:15,028 --> 00:04:17,926 Now we are able to determine the age of the Universe 58 00:04:17,926 --> 00:04:21,511 to within a few million years. 59 00:04:23,705 --> 00:04:27,953 Hubble observed stars with variable brightness — known as Cepheids — 60 00:04:27,953 --> 00:04:29,836 in distant galaxies. 61 00:04:29,836 --> 00:04:34,084 By doing so, astronomers were able to accurately determine 62 00:04:34,084 --> 00:04:37,921 the scale and age of the observable Universe. 63 00:04:40,746 --> 00:04:42,905 Hubble also played a critical role 64 00:04:42,905 --> 00:04:47,005 in one of the most groundbreaking discoveries of the 20th century: 65 00:04:47,005 --> 00:04:50,767 the accelerating expansion of the Universe. 66 00:04:50,767 --> 00:04:53,913 It imaged distant supernova explosions, 67 00:04:53,913 --> 00:04:58,159 and by measuring how bright these explosions appeared to be, 68 00:04:58,159 --> 00:05:03,090 the distances to their host galaxies could be calculated. 69 00:05:05,350 --> 00:05:09,010 Hubble's accurate measurements, not possible from the ground, 70 00:05:09,010 --> 00:05:11,045 were crucial in showing that 71 00:05:11,045 --> 00:05:14,240 these supernovae were fainter than expected, 72 00:05:14,240 --> 00:05:18,578 and so the Universe's expansion must be speeding up. 73 00:05:21,171 --> 00:05:22,516 Astronomers now believe 74 00:05:22,516 --> 00:05:27,113 this expansion is driven by a mysterious dark energy. 75 00:05:29,032 --> 00:05:31,616 With its sharp eye and precise measurements 76 00:05:31,616 --> 00:05:35,116 — made outside Earth’s disruptive atmosphere — 77 00:05:35,116 --> 00:05:38,635 Hubble has revolutionised our knowledge of cosmology 78 00:05:38,635 --> 00:05:41,336 and the evolution of the Universe. 79 00:05:43,456 --> 00:05:44,543 But these are far from 80 00:05:44,543 --> 00:05:47,955 the only important discoveries made by Hubble. 81 00:05:47,955 --> 00:05:52,980 More will be revealed in the second part of this double Hubblecast. 82 00:05:54,067 --> 00:05:57,543 Transcribed by ESA/Hubble. 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