Earth's Tilt 1: The Reason for the Seasons - By MITK12Videos
Transcript
| 00:07 | imagine that you live in north America and one day | |
| 00:10 | you call up your friend in Australia , you guys | |
| 00:13 | are talking and you make plans to go visit him | |
| 00:14 | next summer . So any time next summer works for | |
| 00:17 | you , yep . Whenever is best for you . | |
| 00:20 | Surprised me in a few months , july rolls around | |
| 00:23 | and you hop on a plane for your Australian vacation | |
| 00:26 | . Imagine your surprise when you show up at his | |
| 00:28 | house and he tells you what are you doing Emma | |
| 00:32 | , it's the middle of winter and then you say | |
| 00:34 | winter , it's the middle of summer back in America | |
| 00:37 | and your friends , like I thought I want to | |
| 00:39 | tell you july is winter for us ? Okay , | |
| 00:43 | I don't get this . How can it be summer | |
| 00:45 | in America and winter in Australia at the same time | |
| 00:49 | . That's a great question . I think we can | |
| 00:51 | help you out with that . Yeah . To answer | |
| 00:57 | this question , we have to zoom way back and | |
| 01:00 | start with the top down , look at the Earth's | |
| 01:02 | orbit around the sun . Oh , by the way | |
| 01:05 | , everything you see in this video isn't to the | |
| 01:07 | correct scale . Now the Earth's orbit isn't a perfect | |
| 01:11 | circle . It's actually in the lips . You usually | |
| 01:13 | see it drawn like this . Lots of people think | |
| 01:16 | , hey , this must be why we have seasons | |
| 01:19 | . When the Earth is close to the sun , | |
| 01:21 | we have summer and when the Earth is far away | |
| 01:24 | from the sun , we have winter . But that's | |
| 01:27 | actually not true . If that were true , it | |
| 01:30 | would be summer in America and Australia at the same | |
| 01:33 | time . And we know that's not the case . | |
| 01:36 | Exactly the way we've done our assortment here is really | |
| 01:39 | exaggerated . People just draw it that way to highlight | |
| 01:42 | the extremes . In actuality , there's a relatively small | |
| 01:46 | difference between the Earth's closest and for this point from | |
| 01:48 | the sun . If we draw Earth's orbit with the | |
| 01:51 | correct shape , it looks like this . You can | |
| 01:53 | see it's actually pretty circular but it's not perfect . | |
| 01:57 | So it's not the closeness of the Earth to the | |
| 01:58 | sun that causes the seasons to see what's actually at | |
| 02:01 | work . We have to look at the orbit from | |
| 02:03 | the side in our side view , the Earth is | |
| 02:06 | revolving around the sun in this orbital plane here It | |
| 02:09 | takes one year to go through a full orbit 365 | |
| 02:12 | days . Remember at the same time Earth is rotating | |
| 02:16 | on its axis once every day . The important thing | |
| 02:19 | for the seasons at least is that the Earth actually | |
| 02:22 | isn't straight up and down . It's tilted and the | |
| 02:24 | angle of 23.5 degrees . So when the Earth is | |
| 02:27 | on this side of the sun , the Northern hemisphere | |
| 02:30 | is angled away from the sun . The southern hemisphere | |
| 02:33 | is angled towards the sun . When the Earth is | |
| 02:35 | revolving around the sun , it stays tilted in the | |
| 02:38 | same position , The excess doesn't wiggle around or anything | |
| 02:41 | , it just stays fixed in a certain direction . | |
| 02:44 | So when the Earth is over here , the northern | |
| 02:46 | hemisphere is angled towards the sun and the southern hemisphere | |
| 02:49 | is angled away . When a hemisphere is angled towards | |
| 02:52 | the sun , the sun's rays hit it directly . | |
| 02:55 | That's what's happening in the northern hemisphere here . But | |
| 02:58 | when the hemisphere is angled away from the sun , | |
| 03:00 | like the southern hemisphere here , the sun's rays hit | |
| 03:03 | it indirectly . Okay , so what difference does direct | |
| 03:08 | or indirect sunlight made ? Oh , there's a huge | |
| 03:11 | difference . Let's take a look . With a simple | |
| 03:13 | experiment in this experiment , we're going to use a | |
| 03:17 | flashlight to simulate the sun . Say that the flashlight | |
| 03:20 | is a particular sunday . If it's shining directly , | |
| 03:23 | all its energy is concentrated in a certain area . | |
| 03:27 | But if the sun beam is shining indirectly , the | |
| 03:29 | area is larger . This means that the same amount | |
| 03:32 | of energy is spread out over a larger area . | |
| 03:35 | So in a particular point on the paper , it | |
| 03:38 | feels colder in the indirect Sunbeam than in the direct | |
| 03:40 | sun beam , and the more indirect the Sunbeam , | |
| 03:43 | the larger area . It's important to note that the | |
| 03:46 | amount of energy in the Sunbeam is always the same | |
| 03:49 | . It's not changing . However , if it's spread | |
| 03:52 | out over a larger area , we feel it less | |
| 03:55 | . Let's take a look at what this means for | |
| 03:56 | the earth . Here we have a glove that's angled | |
| 03:59 | at about 23.5°, it's June so the northern hemisphere is | |
| 04:03 | angled towards the sun . If we shine the flashlight | |
| 04:06 | directly on the northern hemisphere , we see it illuminates | |
| 04:10 | a certain area . But when we move the flashlight | |
| 04:12 | to shine indirectly on the southern hemisphere , we see | |
| 04:15 | that it's illuminating a larger area , just like we | |
| 04:18 | talked about . So let's put it all together . | |
| 04:21 | When the northern hemisphere is tilted towards the sun , | |
| 04:24 | it's receiving direct sunlight . It feels warmer , which | |
| 04:27 | we use . It's summer there and the southern hemisphere's | |
| 04:29 | receiving indirect sunlight , which means it feels cooler . | |
| 04:33 | That's winter six months later , when the earth is | |
| 04:37 | on the other side of the sun , we have | |
| 04:39 | the opposite . It's the southern hemisphere receiving direct sunlight | |
| 04:42 | . So it's summer there and the northern hemisphere's receiving | |
| 04:47 | indirect sunlight . So they're having winter . And now | |
| 04:52 | , you know the reason for the seasons awesome . | |
| 04:55 | So it's not how close the earth is to the | |
| 04:57 | sun that matters , but instead it's the tilt of | |
| 05:00 | the earth , which is also wise winter in Australia | |
| 05:04 | at the same time as it's summer in America . | |
| 05:07 | You got it . Well , I think this has | |
| 05:09 | been the most educational vacation I've ever had and there's | |
| 05:13 | so much more to talk about . Did you know | |
| 05:15 | that ? You know , I actually think I'm good | |
| 05:17 | for now . Oh , okay . So would you | |
| 05:21 | like to do now ? We can go bush walking | |
| 05:24 | and bobby I got . |
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