I’m sure you’ve heard people exclaim that the Sun is so hot! You'll hear this quite a bit in the summer time. As expected, you'll hardly hear this repeated in places that experience cold winters. The Sun's a star and it gives us heat and light. Believe it or not, science tells us that the heat that comes off of the Sun is constant and doesn't change in its intensity. So, the amount of heat the Sun gives in January in Chicago is the same as in July in Chicago! Yet, we 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'll need to understand the reasons why temperature differs from place to place and during different times of the year—even in the same places. To better understand that, we can 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 really notice it! Some places receive rain while other places receive snow and even ice. All these things take place in our atmosphere.
In science classes, we learned that the atmosphere is made up of gases, including some that have strange sounding names. Believe it or not, various gases that 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 can run a little bit faster in places where the atmosphere is thinner than in places where it is thicker. That is so because there will be less resistance as you move through the air.
Let's go back to the faithful Sun whose rays remain constant for every day of the year. The rays of the Sun take about eight minutes to reach the Earth. This is because it has to cross about 93 million miles of space to get to us. Think of how quickly those rays must travel in order to get to us in just eight short minutes! Its actual speed is just over 186,000 miles per second! As these rays approach Earth they encounter the outer edges of the atmosphere. Remember the atmosphere is made up of countless particles of gases, dust, and other things.
Think of these particles like sentries of science that 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 return to space. Some of particles will absorb the rays, however. 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. The surfaces then begin to give off this warmth in the form of energy called longwave radiation. Snakes or various other reptiles that depend upon that warmth of their surroundings to get energy understand this real well as you see many of them sitting on the darker colored rocks in the morning. They are enjoying the longwave radiation that is coming from those rocks!
As the surface gives off heat, the air or the atmosphere closer to the Earth’s surface also gets warm. This is how we all stay warm. So the next time you feel like saying, “the Sun is super hot,” why not instead say “all 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 feel 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's remember that the Sun warms the Earth and the Earth warms all air above it. We will unravel more mysteries of different temperatures in later editions of Earth Science: The Planet is Alive.