Why Is the Sky Blue? 16 Kids' Questions About the Sky, Answered
Why is the sky blue and the sunset red? Why does the moon follow our car? Where does space begin? Kids' questions about the sun, moon and sky, answered simply – with experiments to try at home.
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Why is the sky blue? And 15 more big questions
Why is the sky blue? Sunlight looks white, but it is really a mix of all the colors of the rainbow. When it shines into the air, the tiny particles the air is made of bounce the colors around – blue much more than red. So blue light gets scattered all over the sky and reaches your eyes from every direction. That's why the whole sky looks blue!
Fill a clear glass with water, stir in a few drops of milk and shine a flashlight through it in a dark room. From the side, the water looks slightly blue – and when you look through the glass straight into the light, it looks orange, like a sunset.
Why is the sunset red and orange? When the sun is low, its light has to travel a long way through the air to reach you – almost 40 times as far as when the sun stands high overhead. On that long trip, most of the blue light gets scattered away to the sides. What's left for your eyes is mostly red, orange and yellow light. Dust and tiny droplets in the air can make the colors even stronger.
Find out when the sun sets today and watch the sky for half an hour. The colors change from minute to minute: from yellow to orange and red, then pink, purple and deep blue.
Is the sun really yellow? No – the sun is white! It sends out light of every color, and all of them together look white. From space, astronauts see a brilliant white sun. Down here it looks a little yellow because the air scatters away some of its blue light, and when it is low, it turns orange or red. But never look straight at it: it can hurt your eyes!
How does a rainbow happen? A rainbow appears when the sun shines on raindrops. Each drop works like a tiny prism: it bends the white sunlight and splits it into its colors – red, orange, yellow, green, blue and violet. You can only see a rainbow when the sun is behind you and the rain is in front of you. And the lower the sun, the higher the rainbow.
On a sunny afternoon, stand with your back to the sun and spray a fine mist with a garden hose. Move around a little until a small rainbow appears in the water drops.
Why is it dark at night when there are so many stars? At night, your side of the Earth faces away from the sun, out into space. The stars are suns too, but they are so incredibly far away that only a tiny bit of their light reaches us – far too little to light up the sky. So the night stays dark, which is good news for everyone who wants to sleep!
Where does space begin? Space doesn't start at a sharp line: the air just gets thinner and thinner the higher you go. Many scientists say space begins about 62 miles up, at the Kármán line. If you could drive a car straight up at highway speed, you would reach space in about an hour!
Why does the moon follow our car? The moon is so far away – about 239,000 miles – that driving a few miles hardly changes the direction you see it in. Trees and houses by the road are close, so they whiz past. Because everything else moves and the moon stays in the same spot, it looks as if the moon is traveling along with you.
Why can we sometimes see the moon during the day? The moon is up in the daytime just as often as at night – about half the time. It is so close and bright that it shines right through the blue sky. The best time to spot it is around half moon: in the afternoon while the moon is growing, and in the morning while it is shrinking.
Why does the moon look so huge near the horizon? It's a trick your brain plays on you! The moon is just as big low in the sky as high up – in photos it even looks a tiny bit smaller near the horizon. Scientists still argue about why our brain gets it wrong. Probably trees, houses and hills next to the moon make it seem bigger.
When the moon rises, hold a pea at arm's length: it just about covers the moon. Try it again a few hours later, when the moon is high in the sky – the pea still covers it exactly the same way!
How far away is the moon? About 239,000 miles. You could line up 30 Earths side by side in the gap between the Earth and the moon! A car driving nonstop at highway speed would need more than five months to get there. Light is much quicker: it makes the trip in just over one second.
Why don't we fall off the Earth? Because the Earth pulls everything toward its middle – that pull is called gravity. For everyone, everywhere on the planet, "down" means toward the center of the Earth. So people on the other side of the world aren't standing upside down, and the oceans don't pour off into space.
Why does it get dark so early in winter? The Earth is tilted. In winter, your half of the Earth leans away from the sun: the sun climbs less high and takes a shorter path across the sky, so it rises late and sets early. In summer it's the other way around. Near the equator, days are about 12 hours long all year – near the North Pole, the sun doesn't set at all in summer and doesn't rise at all in the middle of winter.
Look up the sunrise and sunset times for your town and write them down once a week. After a few weeks you'll see how much the days grow or shrink!
What are the northern lights? The sun constantly blows tiny particles out into space – the solar wind. The Earth's magnetic field steers some of them toward the North and South Poles. High up in the sky, they crash into the air and make it glow: green, red and sometimes purple. The lights dance across the sky like curtains in the wind.
What is a black hole? A black hole is a place where a huge amount of matter is squeezed into a tiny space. Its pull is so strong that nothing can escape – not even light, which is why it looks completely black. Many black holes form when a giant star dies. But don't worry: the nearest one we know of is about 1,500 light-years away.
Are there aliens? Nobody knows yet! Astronomers have found more than 6,000 planets around other stars, and some of them might have water. Robots search for traces of tiny life on Mars, and there may be oceans under the ice of moons like Europa and Enceladus. So far, no life has been found anywhere except on Earth – but the search goes on.
Will the sun ever burn out? Yes, but not for a very, very long time. The sun is about 4.6 billion years old and has enough fuel for about 5 billion more years. Near the end, it will swell up into a red giant and then shrink into a small, faint star called a white dwarf. That is so far in the future that no one needs to worry.
Why does the moon follow our car?
Press play and ride along: watch the trees, the hills and the moon.
Trees whiz past, hills slide by slowly – and the moon doesn't move at all. It is so far away that driving a few miles makes no difference.