1 00:00:00,000 --> 00:00:06,720 The Sun is our nearest star. 2 00:00:06,720 --> 00:00:08,880 It provides us with warmth and light. 3 00:00:08,880 --> 00:00:12,960 We all know that the Sun is important to life on Earth, but few of us have been given a 4 00:00:12,960 --> 00:00:15,680 good description of the Sun and its composition. 5 00:00:15,680 --> 00:00:20,400 Our Sun is an average star, similar to millions of others in the universe, but it's a big 6 00:00:20,400 --> 00:00:22,320 energy machine. 7 00:00:22,320 --> 00:00:26,700 If you could capture the energy the Sun produces in one second, that would supply the United 8 00:00:26,700 --> 00:00:30,300 States with enough energy for the next 13 billion years. 9 00:00:30,300 --> 00:00:33,300 Where does the Sun's power come from? 10 00:00:33,300 --> 00:00:34,660 Good question. 11 00:00:34,660 --> 00:00:38,980 The basic energy source for the Sun comes from nuclear fusion, and this is when mass 12 00:00:38,980 --> 00:00:42,500 particles combine and tons of energy are released. 13 00:00:42,500 --> 00:00:46,420 The core, or innermost part of the Sun, is made of hydrogen. 14 00:00:46,420 --> 00:00:52,380 The Sun is so dense, and its size is so large, that light released from the core takes about 15 00:00:52,380 --> 00:00:55,860 100,000 years to make its way to the surface. 16 00:00:55,860 --> 00:01:01,420 If the Sun were to stop producing energy today, it would take 100,000 years for significant 17 00:01:01,420 --> 00:01:04,180 effects to be felt at the Earth. 18 00:01:04,180 --> 00:01:07,780 Scientists think there is enough hydrogen on the Sun to continue producing energy for 19 00:01:07,780 --> 00:01:10,060 another 7 billion years. 20 00:01:10,060 --> 00:01:14,260 For many centuries, little was known about the Sun. 21 00:01:14,260 --> 00:01:20,660 However, in the early 1600s, the Italian scientist Galileo used a telescope to take a closer 22 00:01:20,660 --> 00:01:21,900 look at the Sun. 23 00:01:21,900 --> 00:01:25,940 He found dark spots that occasionally appeared and drifted across the Sun. 24 00:01:25,940 --> 00:01:30,340 He also noticed that the dark spots on the Sun's surface were constantly changing. 25 00:01:30,340 --> 00:01:31,340 These are called sunspots. 26 00:01:31,340 --> 00:01:32,340 What are sunspots? 27 00:01:32,340 --> 00:01:35,060 Let's find out. 28 00:01:35,060 --> 00:01:39,420 NASA Goddard's Dr. Eric Christian has some answers for us at the Naval Observatory. 29 00:01:39,420 --> 00:01:40,420 It's a blast! 30 00:01:40,420 --> 00:01:41,420 Thanks, Dan. 31 00:01:41,420 --> 00:01:47,460 The Sun is a fascinating place and a brilliant object to observe. 32 00:01:47,460 --> 00:01:51,380 We observe the Sun through telescopes like this one here at the Naval Observatory in 33 00:01:51,380 --> 00:01:52,380 Washington, D.C. 34 00:01:52,380 --> 00:01:54,740 But satellites help us, too. 35 00:01:54,740 --> 00:02:00,260 To get a better understanding of the Sun, let's look at its different parts. 36 00:02:00,260 --> 00:02:05,220 The visible surface of the Sun, that which we can actually see with the human eye, is 37 00:02:05,220 --> 00:02:07,020 called the photosphere. 38 00:02:07,020 --> 00:02:10,900 Temperatures here are around 6,000 degrees Celsius. 39 00:02:10,900 --> 00:02:15,060 The next two outer layers of the Sun's atmosphere are called the chromosphere and the corona. 40 00:02:15,060 --> 00:02:19,140 The corona is actually hotter than the photosphere at temperatures of 1 to 2 million degrees 41 00:02:19,140 --> 00:02:20,480 Celsius. 42 00:02:20,580 --> 00:02:24,640 The corona is visible to the naked eye during solar eclipses. 43 00:02:24,640 --> 00:02:28,640 Remember the dark spots, or sunspots, that Galileo studied with his telescope? 44 00:02:28,640 --> 00:02:32,440 Well, sunspots are dark, cool areas of the Sun's surface where charged particles are 45 00:02:32,440 --> 00:02:33,440 emitted. 46 00:02:33,440 --> 00:02:37,240 The sunspot only looks dark relative to the brightness of the rest of the Sun, but it's 47 00:02:37,240 --> 00:02:40,920 still pretty hot, 4,000 degrees Celsius hot. 48 00:02:40,920 --> 00:02:44,760 The average sunspot is about the same diameter of the Earth. 49 00:02:44,760 --> 00:02:47,520 Sunspots generate some of the most violent storms in the solar system. 50 00:02:48,400 --> 00:02:52,440 When a sunspot erupts, we call this a solar flare. 51 00:02:52,440 --> 00:02:56,120 Solar flares are some of the biggest explosions in the solar system. 52 00:02:56,120 --> 00:03:01,520 When a solar flare occurs, gas heat of more than tens of thousands of degrees and energy 53 00:03:01,520 --> 00:03:06,200 surpassing billions of atomic bombs is hurled out from the Sun. 54 00:03:06,200 --> 00:03:10,800 Another type of explosion is the CME, or coronal mass ejection. 55 00:03:10,800 --> 00:03:14,720 These explosions can reach speeds of millions of kilometers per hour and can reach the Earth 56 00:03:14,720 --> 00:03:17,680 in just three days. 57 00:03:17,680 --> 00:03:23,520 Both solar flares and CMEs can be very disruptive to human activity on Earth and in space as 58 00:03:23,520 --> 00:03:26,800 these storms, we call them solar storms, travel to the Earth.