I’m sure you’ve heard persons exclaim that the sun is so hot! You hear this quite a bit in the summer time. As expected, you hardly hear this repeated in places that experience cold winters. The sun is a star and gives us heat and light and believe it or not, that heat that comes from the sun is constant and does not change in its intensity. So the same amount of heat that the sun gives in January in Chicago is the same amount of heat that is given in July in Chicago! Yet we all know that the temperatures in Chicago are vastly different during those times of the year. 

There are a few explanations for this but before we can do that, we need to understand the reasons why temperature differs from place to place and during various times of the year in the same place. To understand that, we need to look at a layer of gas that surrounds our planet called the atmosphere. This atmosphere is not uniform and you actually would agree with this when you think about it for a bit. I’m sure you remember feeling sticky and hot and at other times you feel dry and comfortable. The reason for that is that the atmosphere has changed a bit and you notice it! Some places receive rain while other places receive snow and even ice. All these things take place in our atmosphere. 

So the atmosphere is made up of gases of which some are familiar and others have strange sounding names. Believe it or not, the gases which make up our atmosphere have weight! Some parts of the atmosphere have gases that are thick and dense, while other places have less dense gases and the air is quite thin. You will run a bit faster in places where the atmosphere is thin than places where the atmosphere is thicker. That is so because there will be less resistance as you move through the air.

Let us then go back to the faithful sun whose rays remain constant every day of the year. The rays of the sun take about 8 minutes or so to reach our planet. This is so because it has to cross about 93 million miles of space to get to us. Think of how fast those rays move in order to get to us in just 8 short minutes! Their actual speed is just over 186 thousand miles every second! As the rays approach Earth they encounter the outer edges of our atmosphere. Remember the atmosphere is made up of countless particles of gas and dust and other tiny particles. Think of these particles as sentries or soldiers and what they do is stop some of the sun’s rays from reaching the earth’s surface. These rays are called shortwave radiation and some are bounced back by the particles and they go back up to space. Some of the rays are absorbed by these particles as well. Therefore not all of the shortwave radiation that enters our atmosphere actually reaches the surface of the Earth.

The shortwave radiation that eventually reaches the Earth’s surface is absorbed by the material that makes up the Earth making the surface nice and warm. These surfaces then begin to give off this warmth in the form of energy called longwave radiation. Snakes and other reptiles that depend upon the warmth of their surroundings to get energy understand this quite well as you would see many of them sitting on dark colored rocks in the morning. They are enjoying the longwave radiation that is coming from those rocks!

As the surface of the Earth gives off its heat, the air or the atmosphere close to the Earth’s surface becomes warm. This is how we are kept warm. So the next time you feel like saying, “the sun is so hot”, why not say instead “this longwave radiation is killing me!”? Of course, you may ask an obvious question such as: “well why is it so cold in the winter even when the sun is shining?” or some places are hotter than others even though it seems as if the sun is shining at both places?” Those are good questions and there is an explanation for all that too. But for now, let us remember that the sun warms the Earth and the Earth warms the air above it. We will unravel the mysteries of our different temperatures across the planet on the next edition of Earth Science: The Planet is Alive.