1 00:00:00,000 --> 00:00:12,900 Ah, the seasons. It gets cold in the winter, flowers bloom in the spring, we get lots of sun in the summer, and leaves fall in the fall. 2 00:00:15,679 --> 00:00:25,359 See, the Earth's seasons affect every living thing on Earth. That's right, seasons affect the way everything grows and changes every year. 3 00:00:26,039 --> 00:00:29,940 The reason we have seasons on Earth is because the Earth is tilted. 4 00:00:30,620 --> 00:00:32,000 Now let's say that this is the Earth, 5 00:00:32,399 --> 00:00:36,299 and there's an imaginary line going through the middle of it called the Earth's axis. 6 00:00:36,780 --> 00:00:41,079 It's tilted, and it stays tilted as the Earth goes around the sun 7 00:00:41,079 --> 00:00:43,380 at 100,000 kilometers an hour. 8 00:00:43,460 --> 00:00:45,820 That's a billion kilometers every year. 9 00:00:46,439 --> 00:00:49,920 Now not only is the Earth going around the sun, but the Earth is spinning. 10 00:00:50,539 --> 00:00:53,820 And when you're on the part of the Earth that's toward the sun, it's daytime. 11 00:00:53,820 --> 00:00:57,960 And when you're on the part of the earth that's away from the sun, it's nighttime. 12 00:00:58,340 --> 00:01:00,740 Now, the seasons work in kind of the same way. 13 00:01:01,179 --> 00:01:05,159 When the part of the earth that you're on is tilted toward the sun, it's summertime there. 14 00:01:05,519 --> 00:01:10,099 So when it's summertime here at Nye Laboratories, on the other side of the world, it's wintertime. 15 00:01:10,219 --> 00:01:12,939 In places like South America and Australia. 16 00:01:13,019 --> 00:01:14,280 Hey, Bill, your shoe's untied. 17 00:01:14,340 --> 00:01:14,819 Oh, thanks. 18 00:01:17,659 --> 00:01:22,799 Then, when the part of the earth that we're on is tilted away from the sun, it's wintertime here. 19 00:01:22,799 --> 00:01:25,599 And it's summertime on the other side of the world. 20 00:01:25,939 --> 00:01:26,599 Isn't that wild? 21 00:01:27,060 --> 00:01:30,060 All because the Earth's axis is tilted. 22 00:01:30,599 --> 00:01:32,599 That's the reason for the seasons. 23 00:01:33,920 --> 00:01:37,739 Why are the North and South Poles the coldest places on the Earth? 24 00:01:38,280 --> 00:01:40,079 Well, please consider the following. 25 00:01:43,519 --> 00:01:47,180 Let's say that this heat lamp is like the sun, because it's hot. 26 00:01:47,340 --> 00:01:51,840 And let's say that this globe is like the Earth, because it looks like the Earth. 27 00:01:52,319 --> 00:01:55,500 Anyway, we've mounted thermometers on the Earth like this. 28 00:01:55,959 --> 00:01:56,239 See? 29 00:01:56,719 --> 00:01:59,959 Now, the one at the equator is just about off the scale. 30 00:02:00,560 --> 00:02:04,180 And the one at the south pole is right around the room temperature mark. 31 00:02:04,719 --> 00:02:08,659 And the ones in between are somewhere in between. 32 00:02:09,219 --> 00:02:13,819 That's because the heat is hitting the one at the equator almost straight on. 33 00:02:14,159 --> 00:02:17,280 Whereas at the poles, it's just barely grazing by. 34 00:02:17,639 --> 00:02:20,159 And then somewhere in between, well, it's somewhere in between. 35 00:02:20,159 --> 00:02:23,159 You see, it's not that the equator is closer to the heat. 36 00:02:23,539 --> 00:02:26,039 It's that the heat is hitting it more straight on. 37 00:02:26,240 --> 00:02:28,180 See, if the Earth were sitting like this, 38 00:02:28,539 --> 00:02:32,539 then this thermometer would be the hottest and this one would be the coldest. 39 00:02:32,960 --> 00:02:36,939 Anyway, that's why the very warmest places on the Earth are right around the equator, 40 00:02:37,259 --> 00:02:38,979 tropical rainforests and jungles. 41 00:02:39,219 --> 00:02:41,719 And the very coldest places are at the poles 42 00:02:41,719 --> 00:02:46,560 because they're the ones that the energy from the heat lamp just barely grazes by. 43 00:02:46,759 --> 00:02:47,939 I mean the energy from the sun. 44 00:02:47,939 --> 00:02:48,939 I mean, well, anyway. 45 00:02:49,120 --> 00:02:50,039 Thank you for joining me. 46 00:02:51,259 --> 00:02:56,280 Do you notice, though, that the axis about which the Earth turns is not straight up and down. 47 00:02:56,479 --> 00:03:01,020 It's tilted to one side at an angle of 23.5 degrees from the perpendicular. 48 00:03:01,680 --> 00:03:05,819 This has a lot to do with why we have different seasons, as we shall see. 49 00:03:06,960 --> 00:03:10,120 Let's say that this plastic globe of science is like the Earth, 50 00:03:10,580 --> 00:03:13,539 and we have two solar panels mounted on it. 51 00:03:13,539 --> 00:03:18,539 Now, solar panels convert light directly into electricity. 52 00:03:18,539 --> 00:03:22,539 So right now, these two panels are making enough electricity 53 00:03:22,539 --> 00:03:24,539 to run these two little motors. 54 00:03:24,539 --> 00:03:27,539 Now, right now, both motors are going about the same speed. 55 00:03:27,539 --> 00:03:31,539 Now, notice that we have one panel in the northern half of the Earth, 56 00:03:31,539 --> 00:03:33,539 the northern hemisphere, 57 00:03:33,539 --> 00:03:36,539 and one panel in the southern half of the Earth, the southern hemisphere. 58 00:03:36,539 --> 00:03:39,539 They're both receiving about the same amount of light. 59 00:03:39,539 --> 00:03:43,780 But let's say it's summer here at Nye Laboratories 60 00:03:43,780 --> 00:03:46,120 in the northern half of the Earth, the Northern Hemisphere. 61 00:03:46,120 --> 00:03:50,319 That means that the Earth would be tipped toward the Sun 62 00:03:50,319 --> 00:03:58,110 about like, look, the motor in the Southern Hemisphere 63 00:03:58,110 --> 00:04:00,229 is just barely moving, and the motor 64 00:04:00,229 --> 00:04:02,969 in the Northern Hemisphere is spinning like crazy. 65 00:04:02,969 --> 00:04:04,969 Now let's say it's six months later, 66 00:04:04,969 --> 00:04:06,550 and the Earth has gone around the Sun 67 00:04:06,550 --> 00:04:10,189 so that its axis is tipped this way. 68 00:04:10,189 --> 00:04:16,850 Now look, it's reversed. The one in the south is going wild, and the one in the north is 69 00:04:16,850 --> 00:04:24,290 slowed way down. See, what that means is that this panel in the southern hemisphere is receiving 70 00:04:24,290 --> 00:04:28,910 more light, more energy from the sun than the one in the northern hemisphere. It's just 71 00:04:28,910 --> 00:04:35,189 like the Earth's seasons, right here with the Solar Panel Plastic Globe of Science. 72 00:04:35,189 --> 00:04:39,910 Using a flashlight, you can see for yourself that direct rays are concentrated on a smaller 73 00:04:39,910 --> 00:04:44,449 area than planted rays. This is why direct rays produce more heat.