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Blue sky with clouds
The sky can be so many different things: it can be big, beautiful and blue, or grey, cloudy and rainy. It can also be full of stars, or full of orange and red clouds at sunset or sunrise. (Shutterstock)

Curious Kids: What is the sky?

Curious Kids is a series for children of all ages. Have a question you’d like an expert to answer? Send it to CuriousKidsCanada@theconversation.com.

What is the sky? — Pearl, 12, Regina, Sask.

What is the sky really? It’s interesting because the sky can be so many different things to us: it can be big, beautiful and blue, or grey, cloudy and rainy. It can also be full of stars, or full of orange and red clouds at sunset or sunrise.

The reason the sky can appear to be so many different things is because what we perceive as the sky is actually just the different behaviours of a massive layer of gas above our heads. That layer, which we call an atmosphere, is stuck to our planet, Earth, by an invisible force called gravity, and we are at the bottom of it. And depending on the time of day and the conditions in the atmosphere, we will see different things.

As an astrophysicist, I’m particularly interested in the sky, because it’s my job to learn about the different things we find there. I remember the first time I looked at Saturn through a telescope. Normally, when you see Saturn in the sky with your eyes, it looks like a bright star — but when you look at it with a telescope, all of the sudden it’s a whole other world! It blew my mind that it was just hanging out there in the deep vastness of space: I had to learn more.

Bright blues and night time stars

You’ve probably noticed that the sky is especially different between daytime and nighttime, and the reason for that is the sun.

When it’s daytime for us, the side of the Earth we’re on is facing the sun, which means the incredibly bright light that the sun generates is smacking into our atmosphere. The light from the sun is made up of all the colours of the rainbow from red through blue, and our atmosphere is especially good at scattering the blue light. That means when the sun’s light hits the atmosphere, most of it goes straight through, but the blue light is bounced all over the place! So as we sit below our layer of gas, the atmosphere, we see lots of blue light coming from all directions.

Sunset with pink, yellow, blue and orange colours
The light from the sun is made up of all the colours of the rainbow from red through blue. (Unsplash/Quino Al)

At night, however, it’s a different story: the sun is hidden behind the Earth, which means there is no sunlight to be scattered by our atmosphere. This makes the atmosphere mostly invisible to us, and we get to enjoy a beautiful sky full of stars.

This is the sky I really look forward to seeing.

Helping and protecting us

But that’s not all the sky is! It’s also the air we breathe and our protection from space. With each breath, you pull a little bit of the atmosphere into your lungs. We couldn’t survive without it! And that very gas you pull into your lungs is the exact same gas that is responsible for scattering the sun’s blue light to make our sky during the day.

The light we see with our eyes is just one type of light in the universe. There are also X-rays (which we use to look at our bones and teeth), ultraviolet (UV) light, microwaves and radio light (which we use for communication). But we have to be careful, because high energy light, like X-ray or UV light, can be very harmful!

For example, the sun generates a lot of really intense UV light that would burn us very easily if it had the chance. But the atmosphere to the rescue! Our atmosphere is full of a very precious gas called ozone that does a really good job at absorbing solar UV light, and preventing us from getting burnt.

The atmosphere is also really great at burning up small to medium-sized meteors. If we didn’t have an atmosphere, space rocks the size of a car or a bus would just smack into the ground. Our atmosphere, though, acts like a bullet proof vest, burning up these potentially dangerous objects before they get to the ground.

Astronaut in spacesuit floating
Our atmosphere is a big huge layer of gas with lots of different motions. (Unsplash/NASA)

Important, but gets in the way

The funny thing for astrophysicists is that as important as the atmosphere is for us, it actually gets in the way of what we’re trying to do! Let me explain: have you ever swum to to the bottom of a pool, looked up towards the surface, and tried to make out what’s going on above the water? It’s difficult! That’s because the layer of water above you is moving and changing all the time, which is constantly distorting the stuff above the water you’re trying to look at it.

Something very similar is happening on Earth as we look up through our atmosphere to the stars in the night sky. Our atmosphere is a big huge layer of gas with lots of different motions, and we earthlings have our telescopes placed at the bottom of that layer of atmosphere, trying to look through the turbulent atmosphere to the cool stuff beyond.

This is why we place telescopes on the tops of mountains; there’s less atmosphere above us! The ultimate way to get around this is to launch your telescope into space, like the Hubble Space Telescope, or the soon-to-be-launched James Webb Space telescope.


Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsCanada@theconversation.com. Please tell us your name, age and the city where you live. And since curiosity has no age limit — adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.


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