Earth's Tilt 1: The Reason for the Seasons - Free Educational videos for Students in K-12

Earth's Tilt 1: The Reason for the Seasons - By MITK12Videos

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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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