1
00:00:00,120 --> 00:00:01,920
Speaker 1: This Day in History Class is a production of I

2
00:00:02,040 --> 00:00:10,480
Speaker 1: Heart Radio, Hello and Welcome to This Day in History Class,

3
00:00:10,520 --> 00:00:13,600
Speaker 1: a show that reveals a little bit more about history

4
00:00:13,960 --> 00:00:18,800
Speaker 1: day by day. I'm Gay Bluesier, and today we're looking

5
00:00:18,800 --> 00:00:22,840
Speaker 1: at a pivotal moment in astronomical history, the time when

6
00:00:22,920 --> 00:00:26,520
Speaker 1: humans learned that the Earth's moon wasn't the only one

7
00:00:26,560 --> 00:00:39,240
Speaker 1: out there. The day was January seven, six Italian astronomer

8
00:00:39,320 --> 00:00:43,800
Speaker 1: Galileo Galilei made the first recorded sighting of the planet

9
00:00:43,840 --> 00:00:48,920
Speaker 1: Jupiter's moons. He made the discovery using his newly improved

10
00:00:49,040 --> 00:00:54,880
Speaker 1: homemade telescope, which made objects appear twenty times larger. At first,

11
00:00:55,240 --> 00:00:58,720
Speaker 1: Galileo wasn't sure what he was looking at. As far

12
00:00:58,800 --> 00:01:02,360
Speaker 1: as anyone knew, their planets didn't have their own moons,

13
00:01:02,960 --> 00:01:07,039
Speaker 1: So when Galileo noticed three bright lights near Jupiter, he

14
00:01:07,160 --> 00:01:12,759
Speaker 1: just assumed they were distant stars. However, scientists don't let

15
00:01:12,800 --> 00:01:16,200
Speaker 1: assumptions stay assumptions for long if they can help it,

16
00:01:16,560 --> 00:01:20,160
Speaker 1: So Galileo continued observing the lights over the course of

17
00:01:20,200 --> 00:01:23,479
Speaker 1: several nights, and it's lucky for us that he did.

18
00:01:24,240 --> 00:01:28,680
Speaker 1: The discoveries he made that week ultimately changed how humans

19
00:01:28,760 --> 00:01:31,800
Speaker 1: view the universe. As well as our place within it.

20
00:01:32,640 --> 00:01:36,200
Speaker 1: The first thing Galileo noticed was that the three lights

21
00:01:36,280 --> 00:01:40,360
Speaker 1: near Jupiter seemed to move in the opposite direction of

22
00:01:40,400 --> 00:01:44,919
Speaker 1: the stars behind them. The lights also changed their positions

23
00:01:45,000 --> 00:01:48,640
Speaker 1: relative to one another, but always stayed close to Jupiter.

24
00:01:49,440 --> 00:01:52,800
Speaker 1: It was puzzling behavior for a group of stars, so

25
00:01:52,840 --> 00:01:57,600
Speaker 1: the astronomer kept watching. Soon he observed a fourth light

26
00:01:57,720 --> 00:02:01,440
Speaker 1: near the planet that was moving in the same strange way.

27
00:02:01,920 --> 00:02:06,720
Speaker 1: Galileo continued his patient watch for seven straight nights, and

28
00:02:06,800 --> 00:02:11,960
Speaker 1: on January he finally solved the puzzle. The four lights

29
00:02:12,160 --> 00:02:16,840
Speaker 1: weren't stars at all. They were moons or natural satellites

30
00:02:17,200 --> 00:02:20,280
Speaker 1: orbiting the planet Jupiter in much the same way as

31
00:02:20,360 --> 00:02:25,040
Speaker 1: our moon orbits the Earth. This discovery was notable for

32
00:02:25,120 --> 00:02:28,840
Speaker 1: many reasons, but the most important was that it provided

33
00:02:28,919 --> 00:02:35,040
Speaker 1: strong evidence of a heliocentric universe. Up until then, most humans,

34
00:02:35,200 --> 00:02:38,880
Speaker 1: except for Copernicus I, believed the Earth was the fixed

35
00:02:39,000 --> 00:02:42,359
Speaker 1: center of the universe and that all the other celestial

36
00:02:42,440 --> 00:02:46,960
Speaker 1: bodies revolved around it. But the discovery of Jupiter's moons

37
00:02:47,160 --> 00:02:51,359
Speaker 1: through a wrench in that geocentric theory. If moons could

38
00:02:51,480 --> 00:02:55,800
Speaker 1: orbit another planet instead of the Earth, then maybe planets

39
00:02:55,800 --> 00:02:59,400
Speaker 1: could orbit something besides the Earth as well, and if

40
00:02:59,440 --> 00:03:03,359
Speaker 1: that were true, then perhaps Copernicus had been right all along,

41
00:03:03,760 --> 00:03:08,280
Speaker 1: and the Earth really does orbit the Sun. Galileo published

42
00:03:08,320 --> 00:03:13,600
Speaker 1: his discoveries a year later in a book titled Siderius Nuncius,

43
00:03:14,200 --> 00:03:18,000
Speaker 1: or the Starry Messenger. This was the work that set

44
00:03:18,040 --> 00:03:22,160
Speaker 1: Galileo on his path to believing in a Copernican system,

45
00:03:22,200 --> 00:03:25,959
Speaker 1: and his other discoveries of sun spots and solar rotations

46
00:03:26,240 --> 00:03:29,639
Speaker 1: pushed him the rest of the way there. However, when

47
00:03:29,680 --> 00:03:34,680
Speaker 1: Galileo later published his confirmation of the heliocentric theory, he

48
00:03:34,760 --> 00:03:38,880
Speaker 1: was charged with heresies by the Inquisition of the Catholic Church.

49
00:03:39,600 --> 00:03:43,280
Speaker 1: He was found guilty in sixteen thirty three and sentenced

50
00:03:43,280 --> 00:03:47,120
Speaker 1: to life in prison. However, since he was nearly seventy

51
00:03:47,200 --> 00:03:50,520
Speaker 1: years old by that time and in relatively poor health,

52
00:03:50,920 --> 00:03:54,160
Speaker 1: Galileo was permitted to serve out his sentence at home.

53
00:03:55,080 --> 00:03:59,400
Speaker 1: He remained there until January eighth, sixteen forty two, when

54
00:03:59,400 --> 00:04:03,080
Speaker 1: he succumbed to fever and heart palpitations and died at

55
00:04:03,080 --> 00:04:07,480
Speaker 1: the age of seventy seven. In his own time, Galileo

56
00:04:07,720 --> 00:04:11,480
Speaker 1: was unjustly punished for his discoveries, but he's honored for

57
00:04:11,560 --> 00:04:15,400
Speaker 1: them today. The four moons of Jupiter that he discovered

58
00:04:15,600 --> 00:04:20,320
Speaker 1: are now known as the Galilean satellites. In his notebooks,

59
00:04:20,520 --> 00:04:24,440
Speaker 1: Galileo had only referred to the moons numerically as one

60
00:04:24,520 --> 00:04:28,679
Speaker 1: to three, and four, but the German astronomer Johannes Kepler

61
00:04:29,040 --> 00:04:33,200
Speaker 1: recommended naming them after figures from Roman mythology who were

62
00:04:33,240 --> 00:04:36,679
Speaker 1: closely tied to Jupiter, the king of the Roman gods.

63
00:04:37,640 --> 00:04:41,000
Speaker 1: It took more than two hundred years for Kepler's idea

64
00:04:41,080 --> 00:04:44,440
Speaker 1: to gain traction, but he eventually got his wish, and

65
00:04:44,480 --> 00:04:49,880
Speaker 1: the four large moons are now called Io Europa, Ganymede,

66
00:04:50,160 --> 00:04:55,039
Speaker 1: and Callisto. Of course, Jupiter, being the show off planet

67
00:04:55,040 --> 00:04:58,960
Speaker 1: that it is, couldn't content itself with only four moons.

68
00:04:59,520 --> 00:05:04,200
Speaker 1: In the or since Galileo, astronomers have discovered seventy five

69
00:05:04,360 --> 00:05:09,279
Speaker 1: additional moons, bringing Jupiter's grand total to seventy nine moons

70
00:05:09,520 --> 00:05:13,440
Speaker 1: as of two So if you didn't have moon envy before,

71
00:05:13,839 --> 00:05:16,720
Speaker 1: you probably do now. But don't let it get you down.

72
00:05:17,120 --> 00:05:21,359
Speaker 1: Jupiter was just made for moons. Because its mass is

73
00:05:21,400 --> 00:05:25,720
Speaker 1: more than three hundred times that of Earth, Jupiter's gravitational

74
00:05:25,880 --> 00:05:30,320
Speaker 1: field is much larger and stronger too. That enables it

75
00:05:30,400 --> 00:05:34,359
Speaker 1: to capture and hold a lot more satellites in its orbit.

76
00:05:34,800 --> 00:05:38,120
Speaker 1: And gosh, we're all really impressed down here, I can

77
00:05:38,120 --> 00:05:42,799
Speaker 1: tell you. Most of Jupiter's moons are quite small, only

78
00:05:42,839 --> 00:05:47,040
Speaker 1: around six miles or less in diameter. The four moons

79
00:05:47,080 --> 00:05:51,000
Speaker 1: discovered by Galileo or the planet's largest, which is how

80
00:05:51,040 --> 00:05:54,760
Speaker 1: he spotted them through his twenty power telescope. Each of

81
00:05:54,800 --> 00:05:58,720
Speaker 1: the four has its own unique features. For instance, the

82
00:05:58,839 --> 00:06:02,520
Speaker 1: largest of the group, Ganymede, is the only known moon

83
00:06:02,680 --> 00:06:06,599
Speaker 1: to have its own magnetic field, while Callisto is the

84
00:06:06,640 --> 00:06:11,719
Speaker 1: most heavily cratered object in the entire Solar System. As

85
00:06:11,760 --> 00:06:16,359
Speaker 1: for Io, that moon's distinctive feature is the many volcanoes

86
00:06:16,400 --> 00:06:19,159
Speaker 1: that dot its surface, making it one of just a

87
00:06:19,200 --> 00:06:24,760
Speaker 1: few celestial bodies to have confirmed volcanic activity. Last, but

88
00:06:25,080 --> 00:06:30,520
Speaker 1: definitely not least, there's Europa, the smallest of the Galilean satellites.

89
00:06:31,360 --> 00:06:36,640
Speaker 1: Because its entire surface is smooth, uncratered ice, Europa has

90
00:06:36,680 --> 00:06:39,919
Speaker 1: a high degree of reflectivity, making it one of the

91
00:06:40,000 --> 00:06:44,799
Speaker 1: brightest moons in the Solar System. Still, Europa's biggest claim

92
00:06:44,880 --> 00:06:49,240
Speaker 1: to fame is the enticing possibility that a vast ocean

93
00:06:49,400 --> 00:06:53,560
Speaker 1: lies beneath its icy surface, one that might even be

94
00:06:53,680 --> 00:06:59,680
Speaker 1: hospitable to life. Future robotic explorations like NASA's upcoming Europa

95
00:06:59,720 --> 00:07:03,480
Speaker 1: Clip per Mission could supply the answer to that crucial question.

96
00:07:04,120 --> 00:07:08,360
Speaker 1: But like Galileo all those centuries ago, we'll just have

97
00:07:08,400 --> 00:07:13,560
Speaker 1: to be patient and wait and see. I'm Gaye Lousier

98
00:07:13,880 --> 00:07:17,440
Speaker 1: and hopefully you now know a little more about history

99
00:07:17,440 --> 00:07:21,320
Speaker 1: today than you did yesterday. You can learn even more

100
00:07:21,360 --> 00:07:25,840
Speaker 1: about history by following us on Twitter, Facebook, and Instagram

101
00:07:25,880 --> 00:07:29,760
Speaker 1: at t d I HC Show, And if you want

102
00:07:29,760 --> 00:07:32,960
Speaker 1: to commiserate about being stuck on old one Moon Earth,

103
00:07:33,320 --> 00:07:36,200
Speaker 1: you can always drop me a line at This Day

104
00:07:36,240 --> 00:07:40,080
Speaker 1: at i heart media dot com. Thanks as always to

105
00:07:40,240 --> 00:07:43,880
Speaker 1: Chandler Mays for producing the show, and thank you for listening.

106
00:07:44,400 --> 00:07:47,480
Speaker 1: I'll see you back here again tomorrow for another day

107
00:07:47,600 --> 00:07:59,800
Speaker 1: in History Class. For more podcasts from my Heart Radio,

108
00:08:00,120 --> 00:08:02,640
Speaker 1: the I Heart Radio app, Apple Podcasts, or wherever you

109
00:08:02,640 --> 00:08:03,800
Speaker 1: listen to your favorite shows,