In this video, we're going to talk about variation in sunlight angles across latitudes. And so global climate is greatly impacted by the angle at which the sun's rays hit the Earth's surface, which varies across latitudes because the Earth is spherical. Now latitudes are imaginary lines measuring the distance north or south of the equator in degrees, where 0 degrees represents the equator and 90 degrees represents the poles, either the north or south pole. So let's take a quick look at our image down below because we have these very latitudes labeled on the right side. And, again, the equator is the most important latitude that all other latitudes are based on.

It is the midline of the earth, and it separates the earth into the northern and southern hemispheres. Now outside of that, we have the tropic of Cancer and tropic of Capricorn, which appear at 23.5 degrees latitude, and they are important because they define what are known as the tropics, or this tropical region that you can see highlighted here. Now immediately outside of the tropical region, we have the subtropical region, which extends from about 23.5 degrees latitude up to about 35 degrees latitude, and that marks the beginning of the temperate region, which extends from about 35 degrees latitude up to 66.5 degrees latitude. And in the north, we call this the Arctic Circle, and in the south, we call this the Antarctic Circle. So it defines the Arctic and Antarctic regions, which are polar regions where the North Pole and the South Pole can be found.

So make sure to check with your professors which of these latitudes you may be expected to memorize. Now a very important takeaway of this video is that the sun's maximum delivery of heat and energy only occurs when the sun is directly overhead and the sun's rays are hitting the Earth's surface at a 90 degree angle. And this maximum delivery of heat and energy only occurs in regions that are near the equator, and that's going to allow those regions to receive the most direct sunlight angles throughout the year, which is what gives these regions like the tropics relatively hot climate all year round. So notice in the image, we're indicating that the sun is directly overhead giving hot climate here in the tropical regions. And as you move outside of the tropical regions towards the poles in either hemisphere, notice that the sunlight angles get lower and lower, and lower angles of sunlight correspond with colder climates, which is why the poles are associated with cold, climates.

Now another interesting way to look at this image is notice that each of these yellow bars here represents the amount of heat and energy delivered by the sun, and they're all the same height. So they all contain the same amount of heat and energy. However, notice that near the equator, the energy is spread out over a small area, and, therefore, there is a relatively high amount of heat and energy per unit area. But notice that with the lower angles of sunlight, the energy is spread across a larger area, and that means that there's less energy per unit area, and that's also associated with colder climates. So this here concludes our video, and I'll see you all in our next one.