Most of you know that temperatures at the Equator are warmer than they are at the North and South Poles. However, you might not know the exact reason for the the gradient in temperature across the entire globe. After reading this article, you will be able to do a couple of things:

  1. You will be able to explain to your friends why it is hotter at the Equator
  2. You will be able to tell which direction is south during the day time (as long as there are not clouds)

Does that sound like a plan? Okay, let’s learn.

The Earth’s tilt causes the seasons

The first lesson to learn is a common one: The Earth’s tilt causes the seasons. The Earth is tilted at an angle of 23.5 degrees. As the Earth rotates around the sun, the tilt goes from tilting toward the sun in the northern hemisphere (Spring and Summer) to tilting away from the sun in the northern hemisphere (Fall and Winter). The distance of the Earth from the sun does not change the temperature experienced at the surface. In fact, during the summer in the northern hemisphere, the Earth reaches its farthest point from the Sun. The variability of tilt changes the intensity and duration of incoming solar radiation throughout the year.

Graphic showing the Earth’s tilt of 23.5 degrees.

Why is it so hot at the Equator?

The most important phrase for you to take away from this article is angle of incidence. This phrase refers to the angle between the surface of the Earth and the sun. If the sun is directly overhead, then the angle of incidence is 90 degrees. If the sun is just coming over the horizon, then the angle of incidence is near 0 degrees. The angle of incidence is important because the intensity of an energy source, like the sun, is proportional to the angle of incidence.

If the sun is directly overhead, the incidence angle is 90 degrees and the intensity of incoming solar radiation is a maximum. Since the Earth is a sphere, different locations on Earth do not receive the same amount of solar radiation. The Earth receives the most solar radiation at the Equator and the least solar radiation at the Poles. Therefore, the warm temperatures experienced at the Equator are due to the intense solar radiation that is experienced year round relative to the Poles.

Absorption / reflection of sunlight - Understanding Global Change
Difference in solar intensity based on Earth position.

In fact, the Sun’s direct rays (an incident angle of 90 degrees) waffles between 23.5 degrees north (first day of summer in the northern hemisphere) and 23.5 degrees south (first day of winter in the northern hemisphere). Thus, the direct rays of the Sun are never experienced in Youngstown. The largest angle of incidence experienced in Youngstown is during the Summer Solstice when the sun is at an angle of around 72 degrees which provides the most intense solar radiation.

You can use this fact to always orient yourself during the day. Since we know that the Sun’s direct rays are always between 23.5 degrees north and 23.5 degrees south latitude, we know that the position of the sun will always be in the southern sky in Youngstown. Therefore, at solar noon (which depends on the time of year) the sun will be due south of your location. Now you can show off your newfound knowledge to all of your friends.