1 00:00:00,000 --> 00:00:05,000 Okay, let's review. 2 00:00:05,000 --> 00:00:07,000 We've learned about the basic parts of the sun. 3 00:00:07,000 --> 00:00:11,000 We've learned how research scientists study the sun with different types of light radiation. 4 00:00:11,000 --> 00:00:14,000 We've also learned that satellites provide us with this information. 5 00:00:14,000 --> 00:00:18,000 Right, but what if we could see the events leading up to solar storms? 6 00:00:18,000 --> 00:00:22,000 Dr. Michelle Larson from the University of California at Berkeley has the scoop. 7 00:00:26,000 --> 00:00:29,000 What is the goal of the HESI satellite? 8 00:00:29,000 --> 00:00:31,000 When do solar flares occur on the sun? 9 00:00:31,000 --> 00:00:35,000 How do solar flares have a direct effect on the Earth's atmosphere? 10 00:00:36,000 --> 00:00:39,000 Hi, I'm Michelle Larson and I'm an astrophysicist. 11 00:00:39,000 --> 00:00:43,000 An astrophysicist is a researcher who studies physics in space. 12 00:00:43,000 --> 00:00:47,000 I'm here at Vandenberg Air Force Base in California with the HESI satellite. 13 00:00:47,000 --> 00:00:49,000 Let's take a look. 14 00:00:49,000 --> 00:00:52,000 HESI, or High Energy Solar Spectroscopic Imager, 15 00:00:52,000 --> 00:00:57,000 is designed to learn more about the basic physical processes that occur in solar flares. 16 00:00:57,000 --> 00:01:02,000 Teams of astrophysicists and engineers work together to decide what kinds of observations HESI will make 17 00:01:02,000 --> 00:01:05,000 and what kinds of scientific instrumentation will be required. 18 00:01:05,000 --> 00:01:12,000 The HESI teams will achieve their goals by taking pictures of solar flares in the X-ray and gamma-ray radiation range. 19 00:01:13,000 --> 00:01:15,000 What is a solar flare? 20 00:01:15,000 --> 00:01:20,000 Well, remember when Eric told you that solar flares are the biggest explosions in the solar system? 21 00:01:20,000 --> 00:01:25,000 A solar flare occurs when magnetic energy that builds up in the solar atmosphere is suddenly released. 22 00:01:25,000 --> 00:01:29,000 Charged particles, such as electrons, protons, and heavier ions, 23 00:01:29,000 --> 00:01:32,000 travel away from the sun along magnetic field lines. 24 00:01:32,000 --> 00:01:37,000 Others move towards the surface of the sun and emit X-ray and gamma-ray radiation as they slow down. 25 00:01:37,000 --> 00:01:44,000 Flares produce all forms of radiation, from radio waves and visible light to X-rays and gamma rays. 26 00:01:44,000 --> 00:01:46,000 Why study solar flares? 27 00:01:46,000 --> 00:01:51,000 The biggest flares are as powerful as billions of hydrogen bombs exploding at the same time. 28 00:01:51,000 --> 00:01:55,000 We still don't know what triggers them or how they release so much energy in such a short time. 29 00:01:55,000 --> 00:01:59,000 But solar flares have a direct effect on the Earth's upper atmosphere. 30 00:01:59,000 --> 00:02:05,000 For instance, long-distance radio communications can be disrupted by the effect of flares on the Earth's ionosphere, 31 00:02:05,000 --> 00:02:07,000 that is a part of the Earth's atmosphere. 32 00:02:07,000 --> 00:02:12,000 In addition, energetic particles accelerated in solar flares that escape into interplanetary space 33 00:02:12,000 --> 00:02:17,000 are dangerous to astronauts outside the protection of the Earth's atmosphere and magnetic field, 34 00:02:17,000 --> 00:02:20,000 and also to electronic instruments in space. 35 00:02:20,000 --> 00:02:22,000 Where do solar flares occur? 36 00:02:22,000 --> 00:02:25,000 Solar flares occur in the solar atmosphere. 37 00:02:25,000 --> 00:02:29,000 Inside a flare, the temperature is roughly 10 times hotter than the corona, 38 00:02:29,000 --> 00:02:33,000 and can be as high as 100 million degrees Celsius. 39 00:02:33,000 --> 00:02:36,000 The frequency of solar flares varies with the 11-year solar cycle. 40 00:02:36,000 --> 00:02:39,000 At solar minimum, very few flares occur. 41 00:02:39,000 --> 00:02:44,000 As the sun approaches the maximum part of its cycle, they occur more and more frequently. 42 00:02:44,000 --> 00:02:46,000 Let me show you on this graph. 43 00:02:47,000 --> 00:02:51,000 Let's look at the graph of actual solar flare data from 1990 to 2001. 44 00:02:51,000 --> 00:02:55,000 The title of this graph is number of solar flares versus years. 45 00:02:55,000 --> 00:02:58,000 The horizontal axis, or x-axis, represents years, 46 00:02:58,000 --> 00:03:03,000 and the vertical axis, or y-axis, represents the total number of flares recorded. 47 00:03:03,000 --> 00:03:08,000 From the graph, we can see that we have a solar maximum in 1990 and one in 2001. 48 00:03:08,000 --> 00:03:13,000 We have a solar minimum at some point between 1995 and 1996. 49 00:03:13,000 --> 00:03:18,000 This graph shows us that the sun does have a solar cycle, which is about 11 years. 50 00:03:18,000 --> 00:03:22,000 From this graph, we can predict when the next solar maximum and minimum will occur. 51 00:03:22,000 --> 00:03:24,000 How do you study solar flares? 52 00:03:24,000 --> 00:03:31,000 Well, it's actually very difficult to study the high-energy X-rays and gamma rays emitted during solar flares. 53 00:03:31,000 --> 00:03:34,000 To solve this problem, HESI uses a very unique method. 54 00:03:34,000 --> 00:03:38,000 HESI will obtain pictures of solar flares within the X-ray and gamma ray range 55 00:03:38,000 --> 00:03:42,000 by using pairs of metal grids to cast shadows onto detectors. 56 00:03:42,000 --> 00:03:48,000 Each grid is a bit like a fine screen, but with lines running in only one direction, like jail bars. 57 00:03:48,000 --> 00:03:53,000 The solid slats block radiation, and the open slits allow radiation to pass through. 58 00:03:53,000 --> 00:03:57,000 As the satellite rotates at about 15 times per minute, 59 00:03:57,000 --> 00:04:01,000 the grids will allow high-energy X-rays and gamma rays from different parts of the sun 60 00:04:01,000 --> 00:04:06,000 to sometimes pass through and sometimes not, depending on how the slats are oriented. 61 00:04:06,000 --> 00:04:11,000 The HESI detectors will measure the energies of the X-rays and gamma rays that get through 62 00:04:11,000 --> 00:04:16,000 and will record how things change as the satellite, and therefore the grids, rotate. 63 00:04:16,000 --> 00:04:20,000 This is enough information to figure out where the radiation came from on the sun. 64 00:04:20,000 --> 00:04:25,000 This information will be transmitted to the ground, where HESI scientists will use it in their computers 65 00:04:25,000 --> 00:04:28,000 to make pictures of flares in X-rays and gamma rays. 66 00:04:28,000 --> 00:04:32,000 It is like putting together the pieces of a puzzle to figure out what the picture is. 67 00:04:32,000 --> 00:04:36,000 The special way HESI will measure high-energy radiation from the sun, 68 00:04:36,000 --> 00:04:39,000 combined with the way scientists will analyze the data, 69 00:04:39,000 --> 00:04:42,000 will allow us to study the sun in a way never before attempted. 70 00:04:42,000 --> 00:04:47,000 Why will HESI observe the solar flares in the X-ray and gamma ray range? 71 00:04:47,000 --> 00:04:50,000 We know that light emitted in the X-ray and gamma ray range 72 00:04:50,000 --> 00:04:54,000 shows different events than that emitted in the visible light range. 73 00:04:54,000 --> 00:04:58,000 High-energy X-rays and gamma rays carry the most direct information available 74 00:04:58,000 --> 00:05:02,000 about the energetic particle activity on the sun that occurs in solar flares. 75 00:05:02,000 --> 00:05:06,000 With the help of HESI, we will be able to anticipate solar flares, 76 00:05:06,000 --> 00:05:10,000 and HESI will aid in understanding energetic events throughout the universe.