1 00:00:00,000 --> 00:00:07,000 Hi, Dr. D. Hi, kids. I got your email. You must be working on something exciting. 2 00:00:07,000 --> 00:00:10,000 We are planning a trip to the stars. Really? 3 00:00:10,000 --> 00:00:13,000 Well, it's just a school project to design a vacation in space, 4 00:00:13,000 --> 00:00:16,000 but we want to make it as scientifically correct as possible. 5 00:00:16,000 --> 00:00:19,000 We need to know the distances between our destinations and Earth. 6 00:00:19,000 --> 00:00:22,000 Where are you planning to go on your imaginary journey? 7 00:00:22,000 --> 00:00:24,000 The first place is the moon. 8 00:00:24,000 --> 00:00:28,000 Let's see. The moon is about 400,000 kilometers away. 9 00:00:28,000 --> 00:00:32,000 So if there was a road to the moon and you wanted your parents to drive you there... 10 00:00:32,000 --> 00:00:34,000 How long would it take? 11 00:00:34,000 --> 00:00:36,000 A couple of days, maybe a week or two. 12 00:00:36,000 --> 00:00:40,000 If you drive at the speed limit, which on the interstates is about 100 kilometers per hour, 13 00:00:40,000 --> 00:00:44,000 it would take 4,000 hours or more than 165 days. 14 00:00:44,000 --> 00:00:46,000 That's almost six months. 15 00:00:46,000 --> 00:00:48,000 And that's without taking any breaks or sleeping, 16 00:00:48,000 --> 00:00:51,000 not to mention the lack of gas stations along the way. 17 00:00:51,000 --> 00:00:53,000 So how did the astronauts do it? 18 00:00:53,000 --> 00:00:55,000 Well, it only took them about three days, 19 00:00:55,000 --> 00:00:58,000 because they were traveling at thousands of kilometers per hour. 20 00:00:58,000 --> 00:01:00,000 What else might you want to visit? 21 00:01:00,000 --> 00:01:02,000 We were thinking about Mars. 22 00:01:02,000 --> 00:01:07,000 By car, it would take you 64 years when Mars is at its closest. 23 00:01:07,000 --> 00:01:10,000 That's a long time. I think I'd get bored. 24 00:01:10,000 --> 00:01:12,000 Mars is actually a very good choice. 25 00:01:12,000 --> 00:01:14,000 Why is that? 26 00:01:14,000 --> 00:01:16,000 Well, you wouldn't want to go to the other inner planets. 27 00:01:16,000 --> 00:01:19,000 Mercury, the planet closest to the sun, 28 00:01:19,000 --> 00:01:24,000 has a rocky cratered surface that is almost 430 degrees Celsius in the daytime. 29 00:01:24,000 --> 00:01:26,000 Ouch, that's really hot. 30 00:01:26,000 --> 00:01:28,000 Doesn't water boil at 100 degrees Celsius? 31 00:01:28,000 --> 00:01:32,000 Yes, and a very hot pizza oven is about 430 degrees. 32 00:01:32,000 --> 00:01:35,000 Because Mercury doesn't have an atmosphere to retain heat, 33 00:01:35,000 --> 00:01:40,000 at night it can cool to about minus 173 degrees Celsius. 34 00:01:40,000 --> 00:01:42,000 Wow, I'm glad we're not going there. 35 00:01:42,000 --> 00:01:45,000 The next planet out from the sun is Venus. 36 00:01:45,000 --> 00:01:48,000 Its surface is covered with lava flows. 37 00:01:48,000 --> 00:01:51,000 Isn't it also completely covered with clouds? 38 00:01:51,000 --> 00:01:54,000 Yes, its mostly carbon dioxide atmosphere is very dense. 39 00:01:54,000 --> 00:01:57,000 On the surface, it's hot enough to melt lead. 40 00:01:57,000 --> 00:01:59,000 Isn't Jupiter the next planet after Mars? 41 00:01:59,000 --> 00:02:01,000 It is. 42 00:02:01,000 --> 00:02:05,000 Jupiter is over 11 times the diameter of the Earth. 43 00:02:05,000 --> 00:02:08,000 It's mostly made of hydrogen and helium. 44 00:02:08,000 --> 00:02:10,000 It doesn't even have a solid surface. 45 00:02:10,000 --> 00:02:14,000 Saturn, Uranus, and Neptune are also larger than the Earth. 46 00:02:14,000 --> 00:02:18,000 And they are similar to Jupiter in that there is no way to walk on their surface. 47 00:02:18,000 --> 00:02:20,000 But Dr. D., you haven't mentioned Pluto. 48 00:02:20,000 --> 00:02:22,000 That's my favorite planet. 49 00:02:22,000 --> 00:02:25,000 Pluto is very different than the other planets in the outer solar system. 50 00:02:25,000 --> 00:02:27,000 It's small, even smaller than our moon. 51 00:02:27,000 --> 00:02:30,000 Some astronomers think we shouldn't call it a planet. 52 00:02:30,000 --> 00:02:32,000 I wouldn't like that. 53 00:02:32,000 --> 00:02:35,000 Pluto is 15,000 times further away from the Earth than our moon. 54 00:02:35,000 --> 00:02:37,000 And it's very, very cold. 55 00:02:37,000 --> 00:02:41,000 But compared to the nearest star, Pluto is close. 56 00:02:41,000 --> 00:02:43,000 What's the nearest star to Earth? 57 00:02:43,000 --> 00:02:45,000 It's the sun. 58 00:02:45,000 --> 00:02:47,000 Okay, Dr. D., what's the next nearest star? 59 00:02:47,000 --> 00:02:49,000 It's called Proxima Centauri. 60 00:02:49,000 --> 00:02:51,000 And it's 4.2 light years away. 61 00:02:51,000 --> 00:02:53,000 What's a light year? 62 00:02:53,000 --> 00:02:54,000 Let me explain. 63 00:02:54,000 --> 00:02:56,000 Catherine, how far do you live from your grandparents? 64 00:02:56,000 --> 00:02:58,000 About two hours. 65 00:02:58,000 --> 00:03:01,000 You just described the distance with the time, the time it takes to get there. 66 00:03:01,000 --> 00:03:05,000 Light travels at 300,000 kilometers per second. 67 00:03:05,000 --> 00:03:08,000 So it goes about 10 trillion kilometers in a year. 68 00:03:08,000 --> 00:03:10,000 That's what we call a light year. 69 00:03:10,000 --> 00:03:13,000 So if Proxima Centauri is 4.2 light years away, 70 00:03:13,000 --> 00:03:18,000 then it would take us 4.2 years to get there if we were traveling at the speed of light. 71 00:03:18,000 --> 00:03:21,000 Yes, but we haven't even come close to traveling at light speed, 72 00:03:21,000 --> 00:03:23,000 which is the ultimate speed limit. 73 00:03:23,000 --> 00:03:29,000 If you drove your car to Proxima Centauri, it would take over 45 million years. 74 00:03:29,000 --> 00:03:34,000 Even our fastest space probe would take over 60,000 years to get there. 75 00:03:34,000 --> 00:03:37,000 Wow, I had no idea space was so big. 76 00:03:37,000 --> 00:03:38,000 Thanks, Dr. D. 77 00:03:38,000 --> 00:03:39,000 You're welcome. 78 00:03:39,000 --> 00:03:41,000 I have work in my office that I have to do. 79 00:03:41,000 --> 00:03:42,000 You can start your research here. 80 00:03:42,000 --> 00:03:43,000 I'll see you later. 81 00:03:43,000 --> 00:03:44,000 Bye, Dr. D. 82 00:03:44,000 --> 00:03:45,000 Bye.