Up here on the board, we have four circles which represent earth. And so you notice first that the earth does not travel in a circle. It travels in an ellipse.
And so, you think right in the middle of the ellipse, would be the sun. Actually, the sun has shifted over a little bit, so that it’s closer to one part of the ellipse than it is on others.
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So over here we have what we call the perihelion; and over here, we have the aphelion. And so, the parahelion is the closest point to the sun, and the ahelion is the farthest point from the sun. Now in no way is this directly proportional to what it actually looks like. This is just a way to actually give you an idea of what it looks like. So the sun may be shifted a little bit over to the right. And so, the point is here that the earth is closer to the sun in some points than it is in others.
Now you notice here this line right here, which is the way the earth is tilted. So at the top of the earth right here, directly north is right there. Directly south is right there. So really, if the earth would be straight up and down, it would look like that. And so, what we have here is a 23.5-degree angle. I’m going to right that figure right here – 23.5 degrees. Basically, the earth is rotated at an angle of 23.5 degrees. You see that in here, and here, and here each time. It’s rotated 23.5 degrees.
So that’s how we get the different seasons because notice right here, North is pointed away from the sun; but here, North is pointed towards the sun. So right here, when we see North pointed towards the sun, that’s where it’s summer in the Northern Hemisphere. Right here, we have Earth. We have the equator. Up here is the Northern Hemisphere and down here is the Southern Hemisphere. And so everything here is North. Now everything else, the Southern hemisphere, is experiencing winter. All of this area – South America, Australia, is experiencing winter this time because right here is South; and the South is pointed away from the sun. And so, if we’re getting heat from the sun, and the Southern part of the Earth is pointed away, then it’s not getting any sun; or it’s not getting as much sun.
Now over here, we see North pointed away from the sun, the South pointed towards the sun. So it’s now just the opposite thing. The North is experiencing winter; and the South is experiencing summer. And then up here, you may be wondering what that is. So for the whole Northern hemisphere, this is autumn. And for the Southern hemisphere, we have spring down here. So you can see the four seasons right here represented by what part of the Earth is pointed towards the sun. So again, the Earth is always tilted at an axis of 23.5 degrees. So that’s the look at the tilt of earth and the seasons.