What Are Stars? Stars for Kids – Colors, Sizes and Your Birthday Star
Fireflies or giant balls of gas? Explained for kids: what stars are, why they have different colors and twinkle, how enormous some stars are and which star is your birthday star. With hands-on widgets.
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Fireflies or balls of gas?
One night on the savanna, two friends lie in the grass and look up at the sky: a cheeky meerkat and a laid-back warthog. "Those are fireflies stuck up there on the sky," the meerkat explains. But the warthog is sure: they're giant balls of glowing gas, unimaginably far away.
So who's right? The warthog! Stars are giant balls of glowing hot gas, just like our sun. But they don't burn like a campfire: deep inside them, tiny particles fuse together, and that creates enormous amounts of light and heat.
And they really are far away: even the nearest star after the sun is about 25 trillion miles (40 trillion km) away. Fireflies exist too, of course – but they only fly a few feet off the ground.
Why do stars look so small?
Imagine a flashlight shining very far away: from a distance it's just a tiny dot. It's the same with stars. Many of them are bigger and brighter than our sun, but so far away that their light travels for years, hundreds or even thousands of years to reach us.
Stargazing is looking into the past
The light from Sirius, the brightest star in the night sky, takes 8.6 years to reach us. So when you see it today, you see it as it looked 8.6 years ago. With distant stars you even look back hundreds of years.
Our sun is huge – but next to some stars it's a dwarf. Tap your way from small to big: at every step, the one before shrinks to a tiny dot.
Earth: Our home is 7,918 miles (12,742 km) across – huge for us, tiny in space.
The sun: The sun is 109 times as wide as the Earth.
Sirius: Sirius is almost twice as wide as the sun.
Arcturus: Arcturus is 15 times as wide as Sirius – about 16,000 suns would fit inside it.
Rigel: Rigel is a good three times as wide as Arcturus and about 80 times as wide as the sun.
Betelgeuse: Betelgeuse is almost ten times as wide as Rigel. In the sun's place it would swallow Mercury, Venus, Earth and Mars.
Starlight travels for many years to reach us. Somewhere in the sky there is a star whose light set off around the year you were born: your birthday star. How old are you?
You're younger than the light of every star except the sun! Even Alpha Centauri, our neighbor star in the southern sky, is 4.4 light-years away. The sun's light, on the other hand, is only 8 minutes old – so the sun is your star.
Constellations are like connect-the-dots in the sky. Tap the stars in order – and see which shape appears.
The Big Dipper isn't a constellation of its own but the brightest part of the Great Bear. It helps you find the North Star.
Cassiopeia looks like a big W and is in the northern sky all year round. In the old Greek story she was a vain queen.
Orion is the hunter of the sky and easy to see in winter. The three stars in the middle are his belt, red Betelgeuse shines at the top left and blue Rigel at the bottom right.
Why do stars twinkle?
Starlight has to pass through the Earth's blanket of air, and it's always moving: warm and cold air swirl around like the shimmer above a hot road. That makes the tiny dot of light jiggle back and forth. Planets are closer and look like tiny disks, so they hardly twinkle – a good trick for spotting them.
Where are the stars during the day?
Exactly where they are at night! During the day the air spreads the bright sunlight across the whole sky, and that glow outshines the faint stars. In space there's no air to spread the light – there the sky is black even in the daytime.
And what are shooting stars?
Shooting stars aren't stars at all, but specks of dust and tiny pebbles from space. They race into the air at up to 250,000 km/h (155,000 mph) and burn up about 60 miles (100 km) above us. You'll see the most in mid-August and mid-December.
Constellations: connect the dots in the sky
Thousands of years ago people already joined the stars with imaginary lines – into animals, heroes and objects. Today there are 88 official constellations. But the stars of a constellation are usually not close together at all; they only look that way from Earth.
How to find the North Star
Look for the Big Dipper: seven bright stars shaped like a ladle with a long handle. Follow the two stars at the end of the bowl upward about five times their distance, and there shines the North Star. It sits almost exactly above the North Pole and always shows you which way is north.
Stars have a life too
Stars are born in huge clouds of gas and dust and shine for millions or billions of years. Stars like the sun swell up at the end and then become a small white dwarf. Giant stars explode in a supernova, and new stars and planets form from what's left.
And the best part: you're made of stardust! The iron in your blood and the calcium in your bones were made inside stars billions of years ago.
Questions about stars
How many stars are there? In our Milky Way alone there are 100 to 400 billion. In the whole universe there are probably more stars than grains of sand on all the beaches on Earth.
Which star is the brightest? After the sun, Sirius in the constellation Canis Major is the brightest star in the night sky. The planets Venus and Jupiter sometimes shine even brighter – but they aren't stars.
Which star is closest to us? The sun! After that comes Proxima Centauri, 4.2 light-years away. A space probe like Voyager would need more than 70,000 years to get there.
Can stars fall from the sky? No. Stars are enormous and unimaginably far away. What falls from the sky are shooting stars – tiny specks of dust burning up high in the air.
Why is the night sky black if there are so many stars? Because the universe isn't infinitely old: the light of most distant stars hasn't even reached us yet. And many stars are so far away that their light is too faint for our eyes.