How the Sun, the Moon and the Earth work
Light, spin and shadow
Day and night. Summer and winter. A Moon that changes shape, and the rare day the Sun goes dark. All of it comes from one star, two balls of rock, and a few simple facts. Every drawing below is something you can move.
Working out where everything is right now…
Four facts explain it all
You don't need to remember a hundred things about the sky. You need four. Everything else on this page follows from them, and you can test each one with a lamp and a ball.
Or start with a question
Only the Sun shines
The Sun is a star. It is a giant ball of gas so hot that it glows, like the wire in an old light bulb. It makes its own light.
The Earth and the Moon are balls of rock. They make no light at all. We see them only because sunlight lands on them and bounces off. So at every moment, exactly half of each ball is in sunshine, and the other half is in the dark.
Moonlight is just sunlight that has bounced off the Moon and travelled on to us.
TryDrag the Sun anywhere. The bright half of the Earth and of the Moon always turns to face it. Then switch the Sun off.
All the light comes from one place. Every shape, shadow and season on this page is just a question of which half is lit, and who is looking.
Does the Moon make its own light?
No. The Moon is made of grey rock, about as dark as an old road. It looks bright only because the Sun is shining on it and the sky around it is black. If the Sun went out, the Moon would vanish too.
Why is the Sun so hot?
The Sun is so heavy that its own weight squeezes its middle incredibly hard. Down there, tiny bits of gas smash into each other and stick together, and every time they do, a little burst of energy comes out. This happens trillions of times every second. That energy is the Sun's heat and light.
Why mustn't I look at the Sun?
Its light is strong enough to burn the back of your eye in a few seconds. The back of the eye can't feel pain, so you wouldn't even notice it happening. Never look straight at the Sun, not even with sunglasses on.
Day and night
The Earth spins like a top. It turns all the way round once every 24 hours, and that is what we call a day.
The half facing the Sun has daytime. The half facing away has night. As the Earth turns, it carries you out of the dark half into the light (sunrise), across the light (midday), and out the other side (sunset).
So the Sun doesn't really rise or set. It stays where it is. We are the ones turning.
TryPress Play, or drag the Earth to spin it. Watch what you see, and what a friend on the other side of the world sees at the same moment.
Day and night are not something the Sun does. They are something the Earth does.
Where does the Sun go at night?
Nowhere. It is still shining, just on the other half of the world. While you sleep, children on the far side of the Earth are having their lunch.
Why don't we feel the Earth spinning?
Because it turns perfectly smoothly, with no bumps and no sudden stops, and everything turns together: you, the air, your house, the sea. It's like a smooth ride in a plane. You feel it speed up and slow down, but not cruising along. And the Earth never speeds up or slows down. At the equator, the ground is moving at about 1,670 km an hour.
Why can't we see stars in the daytime?
They are still there. The sunlit sky is so bright that it drowns them out, the way a torch is hard to see in a sunny garden. At night our half of the Earth faces away from the Sun, out into space, and the stars appear.
How big, how far
Drawings of space, including most of the ones on this page, squash everything to fit. The real sizes and distances are hard to believe.
The Sun is 109 times wider than the Earth. About a million Earths would fit inside it. The Earth is almost four times wider than the Moon.
And they are very far apart. Thirty Earths in a row would just reach the Moon. The Sun is about 390 times farther away than that.
TryLook at real sizes, then switch to real distances and shine a light from the Earth to the Moon. It moves at the real speed of light.
Now for a lucky coincidence, the one that makes total eclipses possible. The Sun is about 400 times wider than the Moon. It is also about 400 times farther away. Those two cancel out, so from the Earth the Sun and the Moon look almost exactly the same size.
TryDrag the Moon closer to the eye and farther away. On the right, see how big it looks against the Sun.
Big and far looks the same as small and near. That is why the little Moon can cover the giant Sun so exactly.
How long would it take to drive to the Moon?
At 100 km an hour, without ever stopping, about 160 days: more than five months. Driving to the Sun would take about 170 years. The astronauts who went to the Moon got there in three days, because a rocket is much faster than a car.
Why does the Moon look so big when it's low in the sky?
It's a trick your brain plays. Near the ground, the Moon sits next to trees and houses, and your brain decides it must be enormous. Try this: hold your arm out straight and cover the low Moon with your little fingernail. Do it again later when the Moon is high. It's exactly the same size both times.
Is the Sun the biggest star?
No, it's quite an ordinary star. Some stars are so huge that, if one sat where the Sun is, it would swallow the Earth and Mars. The Sun only looks like the biggest because it is by far the closest. All the other stars are so far away that they look like tiny dots.
Why the Moon doesn't fall
Everything pulls on everything else. This pull is called gravity, and the bigger something is, the harder it pulls. The Earth is very big, so it pulls everything towards its middle. That is why a dropped ball falls, and why you stay on the ground.
The Earth pulls on the Moon too. So why doesn't the Moon fall down? It does. It is falling all the time. But it is also moving sideways very fast. In the time it falls a little, it travels so far sideways that the round Earth curves away beneath it. It keeps falling, and it keeps missing. That is an orbit.
TryFire the cannon from the top of a very tall mountain. Then fire again, faster. At just the right speed, the ball falls all the way round the Earth and never lands.
An orbit is falling with enough sideways speed to keep missing the ground. The Moon goes round the Earth like this, and the Earth goes round the Sun.
Why don't people in Australia fall off?
Because "down" means towards the middle of the Earth, wherever you are. For people in Australia, down points to the middle of the Earth too. Nobody is upside down: everybody stands with their feet towards the centre. Press Which way is down? above to see.
Will the Moon ever crash into us?
No. It's actually drifting away, very slowly: about 4 centimetres a year, roughly as fast as your fingernails grow.
How fast are we going round the Sun?
About 30 kilometres every second. That's over 100,000 km an hour, much faster than any rocket. We don't feel it, for the same reason we don't feel the spin: it's perfectly smooth.
Round the Sun, and the seasons
The Earth travels all the way round the Sun once a year. The trip takes 365 days and about a quarter. Those quarters add up, which is why every fourth year gets an extra day, 29 February.
The Earth also leans. The line it spins around, from the North Pole to the South Pole, is tipped over by about 23½°. And it keeps leaning the same way all year long, like a tilted spinning top.
So for half the year, the northern half of the Earth leans towards the Sun. The Sun climbs high, the days are long, and sunlight falls almost straight down. That is summer. For the other half, the north leans away: the Sun stays low, the days are short, and the same sunlight is spread thin over more ground. That is winter.
TryDrag the Earth round the Sun, or press Play. Pick a place. Below, watch how much of its daily circle is in sunlight, how high the Sun climbs at midday, and how spread out its light is.
The seasons come from the lean, not from the distance. In fact, the Earth is closest to the Sun in early January, in the middle of the northern winter.
Is it summer because we're closer to the Sun?
No. Our distance from the Sun changes by only about 3% during the year, and we are closest in January, which is winter in India, Europe and America. The lean matters much more. If distance made the seasons, the whole world would have summer at the same time. It doesn't.
Why is it summer in Australia at Christmas?
When the north leans away from the Sun, the south must lean towards it. So the two halves of the Earth always have opposite seasons. Pick Sydney above and drag the Earth to December.
Why doesn't it snow in Chennai?
Close to the equator, the midday Sun is high in the sky all year, whichever way the Earth is leaning, and the days stay close to 12 hours long. So it is warm all year. The seasons there are mostly about rain, not cold. Compare Chennai with London and Tromsø above.
Why does the Sun shine at midnight in some places?
Near the North Pole in summer, the lean tips that part of the Earth so far towards the Sun that it never turns into the dark half, even at midnight. In winter it stays in the dark for weeks. Try Tromsø in June and December.
Why the Moon changes shape
The Moon travels round the Earth about once a month. The word month even comes from Moon. From one full moon to the next takes 29½ days.
Remember fact one: half of the Moon is always lit by the Sun. The Moon itself never changes. What changes is how much of that lit half we can see from the Earth.
When the Moon is between us and the Sun, its lit side faces away from us and we see nothing: a new moon. When it is on the far side of us, we see its whole lit face: a full moon. In between, we see part of it, a thin crescent, a half, or a fat gibbous moon.
TryDrag the Moon round the Earth, or press Play. On the right is the shape you would see from the Earth.
One more thing to notice: we always see the same face of the Moon, with the same dark patches. That's because the Moon does spin, but slowly. It turns exactly once for each trip round the Earth, so the same side always faces us. Mark a spot on the Moon above and watch it.
The Moon is always half lit. Its phases are just our changing view of that lit half.
Why can I see the Moon in the daytime?
The Moon is in the sky for about half of every day, and it doesn't care whether the Sun is up. A half moon rises around midday, so it's easy to spot in the afternoon sky. Only around new moon is it too close to the Sun to see.
Why does the Moon follow our car?
Because it is so far away. Trees and houses beside the road are close, so they rush past. But you'd have to drive for hours before your direction to the Moon changed even a little. So the Moon seems to keep pace with you, wherever you go.
Is there a man in the Moon?
The dark patches are huge plains of old lava that flowed out and cooled billions of years ago. People around the world see different pictures in them: a face, a rabbit, a woman carrying sticks. What do you see?
Is the far side of the Moon always dark?
No. It gets just as much sunlight as the side we see. At new moon, when our side is dark, the far side is in full daylight. We just never get to see it from the Earth.
The day the Sun disappears
Once a month, at new moon, the Moon passes between the Earth and the Sun. Usually it passes a little above or below the Sun (the next chapters explain why). But sometimes it lines up exactly, and the Moon blocks the Sun. This is a solar eclipse.
Like everything in sunlight, the Moon casts a shadow. Its darkest part is small: only a hundred kilometres or so wide by the time it reaches the Earth. If you stand inside it, the Moon covers the whole Sun. Day turns into deep twilight, the air cools, birds go quiet, and the Sun's glowing outer layer, the corona, appears around a black Moon. This is a total eclipse. People farther away, in the paler part of the shadow, see only a bite taken out of the Sun.
The Moon's path round the Earth is not a perfect circle. When the Moon is farther away, it looks a little smaller than the Sun and can't cover all of it. Then you see a ring of fire: an annular eclipse.
TryPress Play to watch the Moon pass. Drag the little person to stand somewhere else on the Earth. Then move the Moon far away and play it again.
Never look at the Sun, even when it is mostly covered. A thin sliver of Sun is still bright enough to hurt your eyes. Use proper eclipse glasses, or make a pinhole in a card and let it cast a little image of the Sun on the ground. Only during the minutes of totality, when the Sun is completely hidden, is it safe to look directly.
The next solar eclipses
A partial eclipse is visible over a much wider area around each path. Dates from NASA; check a local guide for times where you live.
A solar eclipse is simply standing in the Moon's shadow.
Why do animals act strangely during an eclipse?
The light fades like dusk, but in a few minutes instead of an hour, and it gets cooler. Birds fly home to roost, crickets start chirping, and some flowers begin to close. A few minutes later it's suddenly morning again.
How long does a total eclipse last?
The whole show, from first bite to last, takes two or three hours. But the total part, at any one spot, lasts only a few minutes, never more than about seven and a half. The Moon's shadow races across the Earth faster than a jet plane.
Could I see a total eclipse from my house?
Probably not without travelling. There's a total eclipse somewhere on Earth about every 18 months, but the shadow's path is narrow. Any one spot waits, on average, a few hundred years between total eclipses. That's why people travel across the world to stand in the shadow.
When the Moon turns red
The Earth casts a shadow too, much bigger than the Moon's. At full moon, the Moon is on the far side of the Earth from the Sun. If the three line up exactly, the Moon slides into the Earth's shadow. This is a lunar eclipse.
Everyone on the night side of the Earth can see it at the same time. It is completely safe to watch, and it lasts for hours.
The strange part: the Moon doesn't go black. It turns a deep coppery red. That red light has come through the Earth's air. The air bends a little sunlight round the edge of the Earth and into the shadow, and on the way it turns red, just like the Sun at sunset. During a lunar eclipse, the Moon is lit by all the sunrises and sunsets on Earth at once.
TryPress Play, or drag the Moon through the Earth's shadow. Then press Why red?
The next total lunar eclipses
There are also partial lunar eclipses on 12 January and 6 July 2028. Dates from NASA. The Moon must be above your horizon at the time to see it.
A solar eclipse is the Moon's shadow on the Earth. A lunar eclipse is the Earth's shadow on the Moon.
Why do people call it a blood moon?
Only because of the colour. Nothing happens to the Moon itself. It's the same grey rock, lit by reddish light that has squeezed through the Earth's air.
Why are lunar eclipses easier to see than solar ones?
The Earth's shadow is big enough to swallow the whole Moon, so everyone who can see the Moon sees the eclipse: about half the world at once. A solar eclipse is the other way round. The Moon's shadow is a small spot on the big Earth, so only people inside that spot see the total part.
Why eclipses don't happen every month
If the Moon passes between us and the Sun every month, why isn't there a solar eclipse every month?
Because the Moon's path is tipped. Its orbit is tilted by about 5° compared with the Earth's path round the Sun. Picture two hula hoops, one slightly tipped, crossing at two points. Most months, at new moon, the Moon slips just above or just below the Sun, and its shadow misses the Earth. At full moon, it slips above or below the Earth's shadow.
Things only line up when a new moon or full moon happens near one of the two crossing points. That happens during two short windows each year, called eclipse seasons. It's why eclipses often come in pairs: a solar eclipse and a lunar eclipse about two weeks apart.
TryPress Play to run through a year. Each square below is one new moon or one full moon. Then drag the tilt down to zero, and see what would happen if the hoops were flat.
An eclipse needs two things at once: a new or full moon, and the Moon at a crossing point. That only happens a few times a year.
How many eclipses are there in a year?
Every year has at least two solar eclipses somewhere on Earth, and some years have up to five. Lunar eclipses are similar. Many are only partial, and each one can be seen only from part of the world.
Do eclipses happen at the same time every year?
Not quite. The crossing points slowly creep round, so the eclipse seasons arrive about 19 days earlier each year. After about 18 years and 11 days, the Sun, the Earth and the Moon come back to almost the same arrangement, and a very similar eclipse happens again. People noticed this pattern thousands of years ago and used it to predict eclipses.
A lamp, an orange and a ball
Everything on this page works in your living room. Make the room dark. A lamp with its shade taken off, or a torch on a table, is the Sun.
- Day and night
Put a small sticker on an orange: that's you. Hold the orange near the lamp and turn it slowly, the same way as the drawing in chapter 2. When does your sticker see sunrise? When does it see sunset? Is the lamp moving?
- The seasons
Push a pencil through the orange from top to bottom and tip it a little. Walk slowly round the lamp, keeping the pencil pointing at the same corner of the room. Notice when the top half leans towards the lamp (northern summer) and when it leans away (northern winter).
- The Moon's shapes
Push a ball onto a pencil or stick. Your head is the Earth. Hold the ball out at arm's length, a little higher than your head, and face the lamp. Now turn slowly on the spot, all the way round. Watch the lit part of the ball grow from nothing, to a crescent, to a half, to full, and back again.
- Eclipses
Do it again, but hold the ball exactly at head height. When the ball is in front of the lamp, it blocks it: a solar eclipse. When it's behind your head, your head's shadow falls on it: a lunar eclipse. Now hold it a little higher, as the Moon's tipped path does, and watch it miss both times.
- The real sizes
If the Earth were a marble 1 cm wide, the Moon would be a crumb 3 mm wide, a ruler's length away (30 cm). The Sun would be a ball as tall as a small child (1.1 m), about 118 metres down the road. Try pacing that out in a park.
Everything else children ask
The questions that didn't fit into a chapter. Each answer is short enough to read aloud.
Why is the sky blue?
Sunlight looks white, but it's a mix of all the colours of the rainbow. When it passes through the air, the blue part gets bounced around the most, all over the sky. So wherever you look, blue light is coming at you from the air. On the Moon, which has no air, the sky is black even in the daytime.
Why is the sunset orange and red?
When the Sun is low, its light has to pass through much more air to reach you. By the time it arrives, most of the blue has been bounced away, and the oranges and reds are left. It's the same reason the Moon turns red during a lunar eclipse.
How long does sunlight take to reach us?
About 8 minutes and 20 seconds. So when you see the Sun, you are seeing it as it was 8 minutes ago. Light from the Moon takes just over one second.
Will the Sun ever go out?
Yes, but not for a very, very long time. The Sun has been shining for about 4½ billion years, and it has enough fuel for about 5 billion more. Nobody alive today, or for millions of generations, needs to worry about it.
What colour is the Sun really?
White. It looks yellow from the ground because the air takes away a little of its blue, and orange or red near sunset when the air takes away more. Astronauts in space see a white Sun.
Where did the Moon come from?
Scientists think that long ago, when the Earth was very young, another small planet crashed into it. The crash threw a huge cloud of rock into space, and over time that rock clumped together into the Moon.
Has anyone been to the Moon?
Yes. Twelve astronauts walked on the Moon between 1969 and 1972. Because the Moon has no wind or rain, their footprints are probably still there.
Why does the Moon have holes?
Those round holes are craters, made by space rocks crashing into the Moon. The Earth gets hit too, but our wind, rain and plants wear the marks away. The Moon has no air or weather, so its craters stay for billions of years.
Could I breathe on the Moon?
No. The Moon has no air at all, which is why astronauts wear spacesuits. With no air, there is no sound either, and the sky stays black even in the daytime.
Why is the Moon sometimes orange?
When the Moon is low, its light travels through lots of air, which takes away the blue and leaves orange, just like a sunset. When it climbs higher, it turns white again.
Why is the Earth round?
Gravity pulls everything towards the middle. When something is as big as a planet, its gravity pulls every bit of it in as close to the centre as it can get. The shape where everything is as close to the middle as possible is a ball.
What makes the sea go in and out?
The Moon's gravity. It pulls a little harder on the side of the Earth facing it, and a little less on the far side, so the oceans bulge out on both sides. As the Earth spins, your beach passes through both bulges, so most places get two high tides a day.
If the Earth moves so fast, why don't we fly off?
Gravity holds us down, and the motion is perfectly smooth. Everything around us, including the air, moves along with us. Just as you can pour a drink on a smooth train ride, nothing on Earth notices how fast we're going.
Why is a day 24 hours, a month about 30 days, and a year 365 days?
They all come from the sky. A day is one spin of the Earth. A month was first the time from one new moon to the next. A year is one trip round the Sun. People invented hours, minutes and calendars to divide those up.
One star, two balls of rock
One star that makes light. A spinning Earth that leans. A Moon that circles on a slightly tipped path. And the shadows they cast. Every day and night, every season, every Moon shape and every eclipse comes from those.
Notes on these drawings
Most drawings squash distances so that all three bodies fit; each says so beneath it. The size and distance chapter is to true scale, and its on-screen distances are worked out from the size of your screen, assuming a standard 96 pixels per inch.
The live Moon at the top is calculated in your browser from the date, using a short series for the Sun's and Moon's positions. It is accurate to within a few hours, which is plenty for naming the phase. "You" is placed from your device's clock, so it shows the hour of the day rather than your exact longitude.
In the solar eclipse drawing, the Moon's distance is compressed and its shadow is stretched by the same amount, so the shadow's width where it meets the Earth is to scale (it really is that small). The sky view uses the same numbers: the real sizes and distances of the Sun and the Moon. The lunar eclipse shows the Earth's shadow at its real size at the Moon's distance, but ignores the slight widening caused by the air. The year of eclipses in chapter 9 uses average motions and fixed crossing points, so it shows the pattern, not real dates. The Earth's air, the Sun's glow and the colours are illustrative.
Sources: NASA Sun facts, NASA Moon facts, NASA future eclipses. Updated 8 November 2026.