Beyond Earth
Why This Matters
Have you ever looked up at the sky on a clear night?
If you live far from city lights, you will see thousands of tiny stars. Some are bright. Some are faint. You may see the Moon glowing. It is a beautiful sight. It can make you feel small and full of wonder.
People have looked at this same sky for thousands of years. They were curious, just like you. They asked simple questions. Why does the Moon look different on different nights? Why do stars seem to make pictures? Why does the Sun rise and set?
These were not just fun questions. The answers were useful. Sailors used the stars to find their way at sea. Farmers used the Moon and the Sun to make calendars. They knew when to plant and when to harvest.
In this chapter, we will look up too. We will meet the Moon, the stars, the Sun, and the planets. And we will not just learn what is up there. We will learn why things happen — why the Moon seems to change shape, and why we have day and night. By the end, the sky will make a lot more sense.
The Big Idea
Our Earth is not alone. It is one of eight planets that move around the Sun. The Sun is a star — a giant ball of hot, glowing gas. The Sun makes its own light. But the Moon and the planets do not. They only shine because they reflect the Sun’s light, like a mirror catching sunlight. Almost everything we see in the sky changes in a steady, repeating way — and once you know that the Earth spins and the Moon goes around us, you can explain it all.
Let’s Break It Down
Looking at the night sky
On a clear, dark night, the sky is full of stars.
A star is a huge ball of hot, glowing gas, far out in space. It makes its own light. That is why we can see it shining.
But here is something important. You cannot always see the stars well. If you live in a big city, the sky often looks empty. Why?
The reason is light pollution. This means too much artificial light at night — street lights, signboards, lights from houses and shops. This bright glow fills the sky and hides the faint stars. Smoke and dust make it worse.
In a village, or on a hill far from city lights, the sky is dark. Then you can see many more stars. That is why the best place to watch the night sky is an open, dark area, away from lights, tall buildings, and trees.
Safety first. Never go to a dark, open place at night by yourself. Always go with an adult. After you reach there, wait about half an hour. Your eyes slowly get used to the dark, and then you can see many more stars.
The Moon and its phases — why the Moon seems to change shape
The Moon is our nearest neighbour in space. It is much smaller than the Earth — about one-fourth of the Earth’s width. It has no air and no water. Its surface has many round, bowl-shaped pits called craters (made when space rocks crashed into it long ago).
Now, here is a puzzle. Watch the Moon for a few nights. Its shape seems to change!
Some nights it is a full bright circle. Some nights it is just a thin curve, like a fingernail. Some nights you cannot see it at all. These different shapes are called the phases of the Moon. (“Phase” just means a stage or a form something passes through.)
Figure 12.1 below shows the main phases in a row.
So why does the Moon change shape? Here is the key idea, and it surprises most people.
The Moon does not make its own light. It is not glowing like a star. The Moon shines only because sunlight falls on it and bounces off, like sunlight bouncing off a steel plate.
The Sun lights up exactly one half of the Moon at any time — the half facing the Sun. The other half is always dark. That never changes.
What does change is how much of the lit half we can see from Earth. As the Moon slowly travels around the Earth, we look at it from different angles. Sometimes we see all of the lit half (Full Moon). Sometimes we see only a sliver of it (crescent). Sometimes we see the dark side facing us, so we see nothing (New Moon).
Figure 12.2 below makes this clear.
Now you can see the truth. The Moon’s shape is not really changing. We are just seeing different parts of its bright half. Clever, isn’t it?
On a New Moon night, why can we not see the Moon at all?
Because the Moon is between the Earth and the Sun. So the Sun lights up the far side of the Moon — the side facing away from us. The side facing the Earth is dark. There is no lit part for us to see, so the Moon seems to disappear.
Stars, the Pole Star and constellations
Let us go back to the stars.
Stars look like tiny points of light. But they are actually huge — many are far bigger than our Sun. They look tiny only because they are very, very far away. (Think of a big bus far down the road. It looks small, even though it is huge.)
Here is a wonderful fact: the Sun is a star too. It is the star closest to us. That is the only reason it looks big and bright while the other stars look like tiny dots. The Sun is so close that its light fills our whole sky in the day. That bright sunlight is also why we cannot see the other stars during the day — they are still there, just hidden by the Sun’s glare.
You may have noticed that stars seem to twinkle — their light flickers a little. This twinkling is a handy trick: planets do not twinkle much, so a steady “star” that does not twinkle is often a planet. Why the difference? A star is so far away that it is just a single tiny point of light, and the moving air above us easily makes that point wobble — that wobble is the twinkle. A planet is much closer, so it looks like a tiny disc rather than a single point. The little wobbles across that disc average out, so a planet shines with a steady light.
Long ago, people noticed that some groups of stars seem to make pictures in the sky — a hunter, a bear, a spoon. They joined the stars with imaginary lines (these lines are not really in the sky). Such a group of stars is called a constellation.
One very famous constellation is Ursa Major (the Great Bear). Inside it sits a well-known pattern of seven bright stars called the Saptarishi (also known as the Big Dipper). These seven stars look like a cup with a long handle. So the Saptarishi is not a whole constellation on its own — it is just the brightest, easiest part of the bigger Ursa Major.
The Saptarishi has a special use. It helps you find the Pole Star — a star that hardly seems to move all night. The Pole Star always stays in the North direction. So if you can find it, you know which way is North. This is how travellers and sailors found their direction before maps and the magnetic compass.
Figure 12.3 below shows how to use the Saptarishi to find the Pole Star.
In India, the Saptarishi is named after seven sages, and the Pole Star is called Dhruv Tara. People across the world gave their own names and stories to the same star patterns. The stars are the same — only the stories change.
The Sun, Earth and the Solar System
Now let us meet our Sun’s family.
The Sun is a star — a giant, very hot ball of glowing gases. It is about 100 times wider than the Earth. It gives out a huge amount of heat and light. The Sun is the main source of energy for the whole Earth. Without it, there would be no light, no warmth, and no life.
Around the Sun move eight big objects called planets. A planet is a large, almost round object that moves around the Sun. Our Earth is a planet. The movement of an object around the Sun is called revolution. The Earth takes about one year to go around the Sun once.
The eight planets always go in the same order, from nearest the Sun to farthest. You can learn them in order with a simple sentence — the first letters match the planets:
My Very Easy Method Just Speeds Up Naming → Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Figure 12.4 below shows the Sun and all eight planets in order.
A few nice facts about our neighbours:
- Mars is called the Red Planet, because its soil is reddish.
- Earth is called the Blue Planet, because so much of it is covered with water. From space it looks blue.
- Venus is so bright that people call it the Morning Star or Evening Star — even though it is a planet, not a star.
The Sun, the eight planets, their moons, and many smaller objects (like asteroids and comets) all together are called the Solar System. The Sun is the largest and heaviest member, and it gives almost all the energy to the rest.
There are also some small, round objects that go around the Sun but are too tiny to be counted as full planets. These are called dwarf planets. Pluto is the most famous one — it used to be called the ninth planet, but scientists now group it as a dwarf planet.
What about the Moon? The Moon is not a planet. It is a satellite — an object that moves around a planet. The Moon is the Earth’s natural satellite. It goes around the Earth in about 27 days. (You may notice that one full cycle of phases takes a little longer, about 29 days. That is because while the Moon goes around us, the Earth has also moved along its own path around the Sun — so the Moon needs a couple of extra days to line up with the Sun again.) Some planets, like Jupiter and Saturn, have many moons.
It helps to be very clear about the difference between a star and a planet, and between the Sun and the Moon. The two tables below sort it out.
| Question | Star (like the Sun) | Planet (like Earth) |
|---|---|---|
| Makes its own light? | Yes — it glows on its own | No — it only reflects sunlight |
| What is it made of? | Very hot glowing gas | Rock, or gas and ice |
| Does it twinkle? | Yes, twinkles a lot | No, shines steadily |
| How it moves | So far away that we cannot notice it moving. (Our Sun sits at the centre of the Solar System.) | Revolves around the Sun |
| Question | The Sun | The Moon |
|---|---|---|
| What it is | A star | Earth's satellite |
| Makes its own light? | Yes | No — reflects the Sun's light |
| Goes around what? | It is the centre; planets go around it | Goes around the Earth |
| Gives us | Heat and light (energy) | Light at night (reflected sunlight) |
Day and night — why they happen
Every day the Sun seems to rise in the East, climb up the sky, and set in the West. Then it is night. Then morning comes again. This repeats forever.
It is easy to think the Sun moves around the Earth. But that is not what happens. The truth is the other way around.
The Earth is always spinning, like a top. This spinning is called rotation. The Earth spins once in about 24 hours — that is what we call one day.
Now here is the clever part. The Sun lights up only the half of the Earth that faces it. That lit half has day. The other half faces away from the Sun, stays dark, and has night.
As the Earth keeps spinning, your place moves from the lit half into the dark half, and then back again. So you get day, then night, then day — over and over. The Sun is not really moving across your sky; you are being carried around by the spinning Earth.
Figure 12.5 below shows this.
This is why the Sun seems to rise and set. It is the Earth turning, not the Sun moving. The same spinning Earth also explains why stars fade away at dawn and appear again at dusk.
Let us walk through a careful “why” question, step by step.
It is night-time where you live, but at the very same moment it is daytime in a country on the other side of the Earth. How can it be day and night at the same time?
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First, remember that the Sun lights up only one half of the Earth at a time — the half that is facing it.
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So at any moment, exactly half of the Earth is in light (day) and the other half is in darkness (night). Both happen together, on opposite sides.
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Your country is on the dark half right now, so it is night for you. A country on the far side is on the lit half, so it is day for them — at the very same moment.
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As the Earth keeps spinning, the two halves swap. In a few hours your side will turn into the light (your morning), and their side will turn into the dark (their evening). So it can be day and night at the same time because day and night are simply the two halves of one spinning Earth.
Does the Sun really travel across the sky from East to West during the day?
No. The Sun stays put. The Earth is spinning from West to East. Because we are standing on the spinning Earth, the Sun appears to move across the sky from East to West. It is like sitting in a moving train — the trees seem to rush backwards, but it is really you who are moving.
Common Mistakes
Some ideas about the sky feel true but are not. Let us clear up the most common ones.
The Moon makes its own light, just like the Sun.
The Moon glows brightly in the night sky, and anything that glows in the dark feels like it must be making its own light — a torch, a bulb, a firefly. So it is natural to put the Moon in the same group.
The Moon makes no light of its own. It only reflects sunlight that falls on it, like a mirror catching the Sun. That is also why the Moon seems to change shape — we see different amounts of its sunlit half.
The Sun moves around the Earth — that is why it rises and sets.
With your own eyes, you really do see the Sun move across the sky each day, from East to West. What you see seems to settle the matter, so it feels obvious that the Sun is the one moving.
The Earth is spinning, not the Sun travelling. As the Earth turns once every 24 hours, the Sun only seems to move across our sky. We are the ones being carried around.
Stars come out only at night, and disappear during the day.
You can see stars at night but never in the daytime, so it looks as if they switch off in the morning and switch on in the evening.
The stars are always there, day and night. In the daytime, the Sun's bright light fills our sky and hides the faint light of the other stars, so we just cannot see them.
The Sun is bigger than every other star because it looks so large.
The Sun looks far larger and brighter than any star in the night sky, so it seems to be the biggest star of all.
The Sun only looks big because it is the closest star to us. Many stars in the night sky are actually much bigger than the Sun — they just look like tiny dots because they are extremely far away.
Quick Check
Time to test yourself. Pick the best answer in each question.
Why does the Moon seem to change its shape from night to night?
What causes day and night on the Earth?
Which of these is the correct order of the planets, starting from the Sun?
Which statement about the Sun is true?
Practice Problems
Try each one yourself first. Then tap to check the full answer.
Easy
Name the eight planets in order, starting from the Sun.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. A handy sentence to remember the order: “My Very Easy Method Just Speeds Up Naming” — the first letter of each word matches a planet.
Is the Moon a star, a planet, or a satellite? Explain in one line.
The Moon is a satellite. A satellite is an object that moves around a planet. The Moon is the Earth’s natural satellite — it goes around the Earth in about 27 days.
Why is the best place to watch the night sky an open, dark area away from a city?
Because cities have a lot of artificial light at night — this is called light pollution. The bright glow, along with smoke and dust, hides the faint stars. In a dark area away from lights, the sky is dark, so many more stars become visible.
Medium
The Sun and the stars in the night sky are all stars. So why does the Sun look so big and bright, while the others look like tiny dots?
The Sun looks big and bright only because it is the closest star to us. The other stars are very, very far away, so even the huge ones look like tiny points of light. In fact, many of those distant stars are bigger than our Sun — distance is what makes them look small.
How can you use the Saptarishi (Big Dipper) to find the North direction at night?
First find the Saptarishi — seven bright stars shaped like a cup with a handle. Look at the two outer stars of the cup (the edge away from the handle). Imagine a straight line through them, going outward. Follow that line and it leads to the Pole Star (Dhruv Tara), a star that hardly moves all night. The Pole Star always sits in the North. So once you find it, you have found North.
A friend says, 'The Moon was full last week, but now it is only a thin curve. So the Moon must be getting smaller.' Is your friend right? Explain.
No, your friend is not right. The Moon is not actually getting smaller. The Moon does not make its own light — it only reflects sunlight, and the Sun lights exactly one half of it all the time. As the Moon moves around the Earth, we see different amounts of that lit half. Last week we saw all of it (full); now we see only a thin sliver (crescent). The Moon’s size never changes; only our view of its lit part does.
Challenge
When it is daytime in India, it is night-time in a country on the opposite side of the Earth. Use the idea of the spinning Earth to explain how this is possible.
The Sun can light up only one half of the Earth at a time — the half facing it. So at any moment, half the Earth has day and the other half has night, on opposite sides. India and a country on the far side of the Earth are on these two opposite halves. So when India is on the lit half (day), the far country is on the dark half (night), at the very same moment. As the Earth keeps spinning, the halves swap, and a few hours later India will turn into the dark (night) while the other country turns into the light (day).
Pluto used to be called the ninth planet of the Solar System, but today it is not counted as a planet. What is it called now, and why might scientists have changed their minds?
Pluto is now called a dwarf planet. It lies farther out than Neptune and goes around the Sun, but it is very small — even smaller than our Moon. After Pluto was found, scientists discovered several other small objects out there that were a lot like Pluto. So in 2006, the rules for what counts as a planet were made clearer. By the new rules, Pluto and those similar small objects are grouped together as dwarf planets rather than full planets. Science works like this: when we find new information, we update our ideas.
Summary
Here is what you should now be able to explain in your own words:
- A star is a huge ball of hot, glowing gas that makes its own light. The Sun is a star — the closest one to us — which is why it looks so big and bright.
- The Moon does not make its own light. It shines only by reflecting sunlight.
- The Moon seems to change shape (its phases) because, as it moves around the Earth, we see different amounts of its sunlit half. The Moon itself does not really change.
- A constellation is a group of stars that seems to make a pattern in the sky. The Saptarishi (Big Dipper) helps you find the Pole Star, which always marks the North direction.
- The Solar System is the Sun, the eight planets, their moons, and many smaller objects like asteroids and comets, all together.
- The eight planets in order from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- A planet revolves around the Sun; a satellite (like the Moon) revolves around a planet.
- We have day and night because the Earth spins (rotates) once in about 24 hours — the half facing the Sun has day, the half facing away has night.
What’s Next
That is the end of this chapter — and you have reached the end of your Class 6 Science journey. Well done!
Take a moment to feel proud. You started with the world around you — food, materials, living things, water, magnets, measurement and motion, temperature, separation of substances, and nature’s treasures — and now you have travelled all the way out into space, to the Moon, the Sun, the planets, and the stars. You did not just memorise facts. You learned to ask why, and to find the reason behind what you see.
That habit — asking “but why?” and looking for the answer — is the real heart of science. Keep it with you. The night sky, and the whole world, will always have more to show a curious mind.
When you are ready, go back to the chapter list and revisit any topic you would like to understand even better. Every chapter is here for you, any time. Keep exploring, and keep wondering.
Frequently Asked Questions
Why does the Moon seem to change shape every few days?
The Moon does not actually change shape — it is always a round ball. What changes is how much of the sunlit side we can see from Earth. As the Moon travels around Earth, sometimes we see all the lit side (full moon), sometimes only half, sometimes a thin crescent, and sometimes none at all (new moon). One full cycle of these phases takes about 29 days. These are called the phases of the Moon.
What are the 8 planets in the solar system in order from the Sun?
The eight planets in order from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A helpful trick to remember them is the sentence 'My Very Easy Method Just Speeds Up Naming' — the first letter of each word matches a planet. The first four are small rocky planets and the last four are large gas planets.
Why do we have day and night on Earth?
Earth spins on its own axis — one full spin takes 24 hours. The side of Earth facing the Sun receives sunlight and has day. The side facing away from the Sun is in shadow and has night. As Earth keeps spinning, different places move in and out of sunlight, which is why we have day and night. The Sun itself does not move around Earth — Earth rotates.
What is the Pole Star and why does it not seem to move in the sky?
The Pole Star (also called Polaris) is a star that happens to sit almost directly above Earth's North Pole. Because it is in line with Earth's axis of rotation, it appears to stay still in the sky while all the other stars seem to move in circles around it through the night. Travellers and sailors have used the Pole Star for thousands of years to find which direction is north.
What is a constellation and can you name one class 6?
A constellation is a group of stars that appear to form a pattern or shape when you look at them from Earth. Ancient people named the patterns after animals, people and objects they saw in them. Orion (the hunter) is one of the most famous constellations, easy to spot by three stars in a row forming his belt. Ursa Major (the Great Bear) is another well-known one, and some of its stars form a shape called the Saptarishi or Big Dipper.