Today’s Wonder of the Day was inspired by Vala from Puebla, Mexico, . Vala Wonders, “What do we feel and not see in the air?” Thanks for WONDERing with us, Vala!

When you play games with your friends, do you ever pretend to be ninjas? These nimble warriors move silently and seemingly appear out of nowhere. It's almost like they're invisible!

Ninjas seem to move like the wind. You can't see them, but you can certainly feel their affects when they attack! They remind some people of tornadoes or hurricanes. The destructive winds of these storms remain mostly out of sight until they're upon you.

Have you ever thought much about the air around you? We depend upon air for life. It makes life on Earth possible. It's everywhere all around us all of the time, yet we can't see it. But we can feel it when it moves.

Before we take a closer look at why air is invisible, let's take a moment to be thankful that air is indeed invisible. Can you imagine trying to see your teacher at the front of the classroom if there was a bunch of visible air in the way? How would you ever enjoy watching a movie if you had to peer through a fog of visible air?

Fortunately, most of the time air is invisible. We breathe it in and breathe it out, but we don't have to worry about it getting in the way of seeing the other things around us. This is because the air is made up many different types of gases.

Earth's atmosphere, for example, consists of gases such as nitrogen, oxygen, argon, and carbon dioxide. Unlike solids and liquids, the molecules in a gas are spread far apart. They're also smaller than the wavelength of visible light. This means that light passes through without being reflected or refracted, making air invisible to the human eye.

Occasionally, there may be times when it seems as if you can see the air. For example, when you look up into the sky, it appears blue. From time to time, you can also see fog and rainbows. And what about the Aurora Borealis?

When these phenomena occur, it seems like you can see the air because of light interacting with particles of other materials in the air. For example, fog and rainbows are visible because light is reflected and refracted by particles of water vapor in the air.

When you look up at a blue sky, you can see light reflecting back from particles that are high in the atmosphere and thus closer to the Sun. As you bring your eyes downward away from the upper atmosphere, you can see the color of the sky change from blue to the invisible air in front of you.

As far as the Aurora Borealis is concerned, the unique, shimmering lights that occur during the phenomenon are truly spectacular. It really does seem like the air itself becomes visible and even colorful. As with the other examples, the Aurora Borealis occurs because of light interacting with electrically-charged particles in Earth's magnetosphere.

Even if you can't see the air around you, you can feel it, especially when it moves against you when the wind blows. When this happens, the gas molecules are pushed against your skin. When enough of them move against your skin, you feel it is a slight breeze.

Even when it seems like you can't feel the air around you, it's always pushing down on you. The weight of all the air around and above you is quite significant. At sea level, the atmosphere pushes down on you with a weight of approximately 14.7 pounds per square inch. You don't feel this weight as a burden, though, because the air inside of you pushes back with an equal force.

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We don’t mean to bug you, but we sure hope you’ll join us in Wonderopolis tomorrow!