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Cosmology and astronomy
Course: Cosmology and astronomy > Unit 3
Lesson 3: Earth's rotation and tilt- Seasons aren't dictated by closeness to sun
- Season simulator
- How Earth's tilt causes seasons
- Are southern hemisphere seasons more severe?
- Milankovitch cycles precession and obliquity
- Precession causing perihelion to happen later
- What causes precession and other orbital changes
- Apsidal precession (perihelion precession) and Milankovitch cycles
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Are southern hemisphere seasons more severe?
Are Southern Hemisphere seasons more severe because of the eccentricity in Earth's orbit? Created by Sal Khan.
Want to join the conversation?
- If you are at the equator then are there any seasons since that January is Nth Hemi Winter and Sth Hemi Summer. I dont get ca someone explain everything in season related about the equator.
Like so people know and my self! :P(7 votes)- I'm not the best at seasons when it comes to equators, but I can try my best to explain it to you. As you get closer to the equator, you will begin to feel less and less seasons, due to the fact that the Sun stays the same eight everyday. If the Northern Hemisphere is Winter and the Southern Hemisphere is Summer, then the equator would be experiencing something similar to a combination of Autumn and Spring, though more towards Spring because of the extreme weather near the equator.(4 votes)
- i m getting confused with the earth's tilt.if earth revolves around the sun in an anticlockwise direction and the earth axis is inclined at 23.5deg from vertical,which way should the tilt be during its revolution around the earth.(6 votes)
- I guess you meant: Which way should the tilt be during its revolution around the sun.
During summer on the northern hemiphere, the tilt is towards the sun, during winter away from the sun.(2 votes)
- Why is there a hole in the atmoshpere?(11 votes)
- its not "cars and coal factories burn fossil fuels" its because of chemicals called Chlorofluorocarbons (CFCs) which breakdown ozone(10 votes)
- This for some reason reminds me of an unrelated question, but is it true that gravity is a fictitious force and doesn't really exist? (I think this relates more towards Special Relativity, but it's been on my mind for a while)(4 votes)
- Pick up an object, and let go of it. Did it fall?, gravity is a real force.(4 votes)
- what happens when you have hole in the atmosphere, does radiation fall through?(4 votes)
- There is no hole in the atmosphere. There is a hole in the ozone layer of our atmosphere (centered above Antarctica). This hole does allow more UV radiation to penetrate to the surface of Earth.(5 votes)
- 1) when perihelion occurs(jan 3rd) which hemisphere is getting more solar radiation according to tilt of earth?
2) according to kepler's law the orbit of each planet is an ellipse with the sun at one of the foci.(5 votes)- I'd like to add to the question......
Circumference of Earth at Equator = 40,075 km ............. Axial Tilt = 23.4°
Perihelion = 0.98329 AU or 147,098,070 km (early January)
Aphelion = 1.01671 AU or 152,097,700 km (early July)
So the tilt away from the Sun of a 40,000 km object (Earth) has a greater effect on the temperature than 5,000 km in distance? What distance is created by the tilt?(2 votes)
- Why is Earth's orbit not a complete circle and what makes it not a complete circle?(3 votes)
- A perfectly circular orbit is unstable, any slight disruption in the orbit will cause it to become an ellipse.(4 votes)
- If the Earth's orbit was more elliptical (bigger difference between perihelion and aphelion), then would there be an effect on how moderate the seasons would be?(2 votes)
- There would be an additional complicating factor in the earth's seasons, because there would be two things causing seasons rather than one. We would have one sort of summer due to the perihelion and then another sort due to the tilt, and sometimes they might match up and other times they wouldn't. Astronomers would have a lot of fun working out calendars to forecast the seasons to come.(3 votes)
- If the distance from the Earth to the Sun is one AU. At what point during the year would the astronomical unit be precise if the distance is constantly changing?(2 votes)
- Usually, the earth is exactly 1 AU from the sun in autumn and spring.(2 votes)
- I was wondering if the south pole being 3% closer to the sun during its summer than the north pole is during its summer has any bearing on the ozone depletion (hole) over the south pole being bigger than over the north pole, or is this more likely to be due to other factors like air currents?(2 votes)
Video transcript
In previous videos we've
already talked about the idea that there are times
in Earth's orbit when it is closer
to the sun and when it is farther from the sun. And when it is
closer to the sun, so let's say that this is the
time in the orbit when it's closer to the sun,
this is the perihelion. And when it's
farthest from the sun, and I'm exaggerating the
difference, this is aphelion. This is the aphelion
in our orbit, when we are farthest
from the sun. And maybe our orbit looks
something like this. I shouldn't have the
bulge over there. So maybe our orbit looks
something like this over here. And what I point out in the
first video where we discuss this is that this is not
the cause of the seasons. Even though we are 3% closer
right now, the way our orbit is set up, and we'll
see in future videos that the difference or
the eccentricity, or how elliptical the orbit is,
does change over time, how much it deviates
from being circular. That's one way to think
about eccentricity. That does change over time. But right now when we
are closest to the sun we are 3% closer than when
we are farthest from the sun. So 3% closer than at aphelion. And we point out in the first
video when we discussed this that this is not the
cause of the seasons. And in particular, perihelion
, when we were closest to the sun, when we actually
have the most radiation from the sun, that's actually when
we have the Northern Hemisphere winter. So this occurs right over here. This occurs in January. And aphelion occurs in July. Now, based on this,
this might lead to an interesting question,
because let's think about January when
we're at perihelion, and let's think about July
when we're at aphelion. Let me draw a quick
globe right over here. And let's make that the equator. And I'll draw it
in both situations. So January is obviously when
we have the Northern Hemisphere winter. So I'll paint it in
blue right over here. It is winter. And July is when we have
the Northern Hemisphere summer, or the Southern
Hemisphere winter. So then we have
winter during July in the Southern Hemisphere. And let me put summer
in a more summery color. I guess that orange is
a pretty good color, but that's not orange. Here's orange. All right. That's orange. And that's orange. So these are summer. So that's the summer in the
Southern Hemisphere, which occurs during the winter the
Northern Hemisphere, and vice versa. Summer in the
Northern Hemisphere occurs during winter in
the Southern Hemisphere. And so the question might
be rising in your head, and I did see a few comments
on that first video asking this question, and
it's a good one. If we are closer to
the sun in January, or we are closest to
the sun in January-- this is the perihelion
right over here-- and so we are getting more
solar radiation in January, does that moderate the winter? Does that moderate the winter
in the Northern Hemisphere? Or I guess another
way to think about it, does it make the summer
in the Southern Hemisphere when we are closer to
the sun, does it make it more extreme, or hotter? And vice versa, in July, when
we are farthest from the sun, does that moderate the
Northern Hemisphere winter? Because it's hot
out there, but hey, we're little bit
farther from the sun. And does it make the Southern
Hemisphere winter colder? So once again does it
make this more extreme? Because it's already winter
and we're farther from the sun. So maybe we're also
getting less radiation. And so there's a couple
ways to think about it. One, it is true that
when we're farther we are getting a little bit
less radiation from the sun or we're getting heated
up a little bit less. But the one reality is that
the Southern Hemisphere climate as a whole is not more
extreme despite getting more solar energy in
the summer and getting less solar energy in the winter. And the reason why it
is not as extreme-- Let me draw the
equator here just so we can separate
our hemispheres. The main reason it is believed
that it is not more extreme is that the Southern Hemisphere
has a lot more water in it. So just if you look at the
surface of the Southern Hemisphere you're looking
at a lot more water than the surface of the
Northern Hemisphere. And this is, of course,
it's a Mercator projection, and so it distorts things so
that things near the poles get really kind of built
up to look really huge even though they really
aren't that big. Greenland really isn't
larger than South America. It just spreads them out so
that you can kind of flatten out the map, so to speak. But the Southern
Hemisphere has more water, and as you may have
learned in chemistry class, water has a higher
specific heat. It takes a higher specific
energy, more heat, to raise water a degree than
it does to raise land a degree. And so water can
absorb more energy. Or when there's
less energy, water will release more energy
without dropping as much of a temperature. So water has a moderating
influence on the climate. So even though the summers
in the Southern Hemisphere actually are getting
more radiation than the summers in the
Northern Hemisphere, it's moderated on the
actual temperature because the water
has the ability to absorb more of that
heat without changing the temperature as dramatically. Now, with that said, it is
true that in general Antarctica is colder. Antarctica is colder
than the North Pole. But the main reason
why Antarctica is colder, besides the
fact that it's on land, as opposed to the
North Pole being in the center of
the Arctic Ocean, is that it's actually a huge,
very high altitude ice sheet. And so the altitude
for most of Antarctica is around 8,000 feet. So it's kind of like
an alpine altitude. So the main reason
why it's colder is possibly being farther
away from the sun in winter might play some role there, but
the main reason why it's colder is it is just at a
much higher altitude, and it's to some degree
insulated from the water, or I guess you could
say it's on the land. So especially during
the long winters it's going to get
that much colder. But I'll leave you there,
and to some degree, and this is the other aspect
of it, during the summers-- And all of this stuff
is super complicated. So you can't just draw
out one rule of thumb and say this is the reason. But these are all
the influences-- is that if you have a
super large ice sheet it's also more likely to
reflect more of the energy because it's white,
as opposed to a darker color like the
ocean or the land. And so you can think about
all of those factors, but the general answer
is it's a good question. But overall, the climate
in the Southern Hemisphere is not more extreme than
the climate in the Southern Hemisphere, even though
Antarctica is colder.