Stars and planets
On a clear night you see many dots in the sky. Most of them twinkle, but one bright dot, often Venus, shines steadily. The twinkling ones are stars and the steady ones are planets.
The sun, moon, stars and planets are heavenly bodies (आकाशस्थ पिंड). Stars (तारे) have their own light and twinkle. Planets (ग्रह) have no light of their own and do not twinkle.
Rule 1: Stars and the sun — A star makes its own light, like a lamp. The sun is a star. It looks big and bright only because it is the nearest star to us.
- Easy : Easy: The sun is a star.
- Medium : Medium: Other stars look tiny dots because they are very far away.
- Exam-type : Exam: Why does the sun look bigger than other stars? Because it is closest to us.
Rule 2: Planets — A planet is like a mirror: it only shines by the sun's light falling on it. So planets do not twinkle.
- Easy : Easy: Venus is a planet and does not twinkle.
- Medium : Medium: Planets get light from the sun.
- Exam-type : Exam: Give one difference: a star twinkles, a planet does not.
Star = own light, twinkles. Planet = no own light, steady.
Thinking the sun is not a star. It is the star nearest to us.
Memory clue: "तारा लुकलुकतो, ग्रह स्थिर".
Spot the difference
| Feature | Star | Planet |
|---|---|---|
| Own light | Yes | No |
| Twinkles | Yes | No |
| Example | Sun | Earth, Venus |
Practice questions
- 1Name two heavenly bodies.
- 2Which has its own light: a star or a planet?
- 3Is the sun a star or a planet?
- 4Which one twinkles?
- 5Where do planets get their light from?
- 6Why does the sun look big and bright?
- 7A bright dot in the sky does not twinkle. Is it more likely a star or a planet? Why?
- 8Why do stars other than the sun look like tiny dots?
Show answers (try them yourself first)
- 1Sun and moon (or any star or planet).
- 2A star.
- 3A star.
- 4A star.
- 5From the sun.
- 6It is the star closest to us.
- 7A planet, because planets shine steadily.
- 8They are very far away.
The solar system
Imagine children running in circles around a tree in the school ground. The tree stays in the middle and the children go round it again and again. The planets go round the sun in the same way.
The earth's movement around the sun is its revolution (परिक्रमा) and the path is its orbit (कक्षा). The sun and the bodies that revolve around it form the solar system (सूर्यमाला).
Rule 1: The eight planets — The planets in order from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Besides the earth there are seven other planets. The earth is the third.
In the figure : In the figure the eight planets in order from the Sun, with the asteroid belt between Mars and Jupiter.
The solar system
In the app you can move this figure with your finger.
Open in the app- Easy : Easy: The planet nearest the sun is Mercury.
- Medium : Medium: Mars comes right after the earth.
- Exam-type : Exam: Which planet is the fifth from the sun? Jupiter.
Rule 2: Revolution and orbit — Every planet goes round the sun along its own fixed orbit. The earth takes one year to complete one revolution.
- Easy : Easy: The path of a planet is its orbit.
- Medium : Medium: One revolution of the earth makes one year.
- Exam-type : Exam: The sun and the bodies that go round it together form the solar system.
Eight planets; earth is third from the sun. Revolution = going round the sun; orbit = path.
Saying there are eight planets besides the earth. There are seven others.
Memory clue: "My Very Educated Mother Just Served Us Noodles" gives Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune in order.
Spot the difference
| Term | Meaning |
|---|---|
| Revolution | Going round the sun |
| Orbit | Path of revolution |
| Solar system | Sun and bodies going round it |
Practice questions
- 1How many planets are there in the solar system?
- 2Which planet is nearest to the sun?
- 3What is an orbit?
- 4What is revolution?
- 5Which is the third planet from the sun?
- 6How many planets are there besides the earth?
- 7Name the planets between Earth and Jupiter.
- 8Write the eight planets in order from the sun.
Show answers (try them yourself first)
- 1Eight.
- 2Mercury.
- 3The path along which a planet goes round the sun.
- 4The movement of a planet around the sun.
- 5The earth.
- 6Seven.
- 7Mars only (the asteroid belt lies between Mars and Jupiter).
- 8Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Satellites, dwarf planets and asteroids
At night the moon follows you as you walk. In truth the moon goes round the earth, and the earth goes round the sun.
A satellite (उपग्रह) revolves around a planet. A dwarf planet (बटू ग्रह) is a small body going round the sun on its own. Asteroids (लघुग्रह) form a band between Mars and Jupiter.
Rule 1: Satellites — The moon is the earth's satellite. It gets its light from the sun. It looks big only because it is the nearest body to us, though it is much smaller than the sun.
In the figure : In the figure the Earth goes round the Sun in its orbit, and the Moon, a satellite, goes round the Earth.
- Easy : Easy: The moon is the earth's satellite.
- Medium : Medium: The moon gets light from the sun.
- Exam-type : Exam: The moon looks big because it is near, not because it is bigger than the sun.
Rule 2: Dwarf planets and asteroids — Pluto is a dwarf planet. It goes round the sun on its own. Asteroids are small rocky bodies in a band between Mars and Jupiter, and they also go round the sun.
- Easy : Easy: Pluto is a dwarf planet.
- Medium : Medium: Asteroids lie between Mars and Jupiter.
- Exam-type : Exam: A dwarf planet goes round the sun, but a satellite goes round a planet.
Satellite goes round a planet. Dwarf planet and asteroids go round the sun.
Saying the moon goes round the sun alone. It goes round the earth.
Memory clue: "उपग्रह = ग्रहाचा साथीदार".
Spot the difference
| Body | Goes round | Example |
|---|---|---|
| Satellite | A planet | Moon |
| Dwarf planet | The sun | Pluto |
| Asteroids | The sun | Band between Mars and Jupiter |
Practice questions
- 1What is the earth's satellite?
- 2What does a satellite go round?
- 3Name a dwarf planet.
- 4Where are the asteroids found?
- 5From where does the moon get its light?
- 6The moon is smaller than the sun. Why does it look big?
- 7How is a dwarf planet different from a satellite?
- 8Which body goes round the earth, and which body goes round the sun with the earth?
Show answers (try them yourself first)
- 1The moon.
- 2A planet.
- 3Pluto.
- 4In a band between Mars and Jupiter.
- 5From the sun.
- 6It is much nearer to us.
- 7A dwarf planet goes round the sun on its own; a satellite goes round a planet.
- 8The moon goes round the earth; the earth itself and other planets go round the sun.
Gravity
When you throw a ball up, it always comes back down. A mango falls from the tree to the ground, never upward. Something pulls things towards the earth.
All heavenly bodies pull one another with the force of gravity (गुरुत्वाकर्षण).
Rule 1: Gravity on the earth — The earth's gravity pulls things down. That is why things stay on the earth and fall downwards.
- Easy : Easy: A dropped pencil falls down.
- Medium : Medium: Rain drops fall down because of gravity.
- Exam-type : Exam: Why do we not fall off the earth? Because gravity holds us.
Rule 2: Gravity in the sky — The sun pulls the planets, and a planet tends to move away. Because of both, each planet stays in its fixed orbit.
- Easy : Easy: The sun pulls the planets.
- Medium : Medium: The earth pulls the moon, so the moon stays near it.
- Exam-type : Exam: Without the sun's pull, planets would move away in a straight line.
Gravity is a pull between heavenly bodies. It keeps things on the earth and planets in orbit.
Thinking only the earth has gravity. Every heavenly body pulls others.
Memory clue: "गुरुत्व = ओढ".
Spot the difference
| Where | Gravity does |
|---|---|
| On earth | Pulls things down |
| In the solar system | Keeps planets in orbit |
Practice questions
- 1What is gravity?
- 2Why does a dropped ball fall down?
- 3What keeps the planets in their orbits?
- 4Does only the earth have gravity?
- 5Why do things stay on the earth?
- 6Why does the moon stay near the earth?
- 7A ball thrown upward comes back. Explain.
- 8What would happen to a planet if the sun's pull stopped?
Show answers (try them yourself first)
- 1The pull between heavenly bodies.
- 2The earth's gravity pulls it.
- 3The sun's pull (gravity).
- 4No, all heavenly bodies have it.
- 5Gravity pulls them down.
- 6The earth pulls it by gravity.
- 7Gravity pulls it back to the earth.
- 8It would move away from its orbit instead of going round the sun.
Space travel and India's missions
A mobile network, TV channels and weather forecast on your phone all depend on satellites that people sent into space. Sending them up needs rockets.
To reach space a spacecraft must overcome gravity. Rockets (रॉकेट) give the needed power.
Rule 1: India in space — Rakesh Sharma (1984) was the first Indian in space. He flew on the Soviet craft Soyuz T-11, launched on 2 April 1984. When Prime Minister Indira Gandhi asked how India looked from space, he replied "Saare Jahan Se Accha".
- Easy : Easy: The first Indian in space was Rakesh Sharma.
- Medium : Medium: He went in 1984.
- Exam-type : Exam: Who was the Prime Minister when Rakesh Sharma was in space? Indira Gandhi.
Rule 2: Moon and Mars missions — Chandrayaan-1 went to the moon on 22 October 2008; its instruments later helped detect water on the moon. Mangalyaan (M.O.M.) was launched in November 2013 and reached the orbit of Mars on 24 September 2014 in the very first attempt. Years later, in August 2023, Chandrayaan-3 landed near the moon's south pole.
- Easy : Easy: Chandrayaan-1 went to the moon.
- Medium : Medium: Mangalyaan reached Mars in its first attempt.
- Exam-type : Exam: Man-made satellites help in farming, weather forecast, maps and telecommunication.
Rocket = power to leave earth. Rakesh Sharma 1984; Chandrayaan-1 2008; Mangalyaan 2014.
Mixing up the missions. Moon = Chandrayaan, Mars = Mangalyaan.
Memory clue: "चांद्रयान चंद्राला, मंगळयान मंगळाला".
Spot the difference
| Mission | Year | Goes to |
|---|---|---|
| Rakesh Sharma | 1984 | Space |
| Chandrayaan-1 | 22 Oct 2008 | Moon |
| Mangalyaan | 24 Sep 2014 | Mars |
Practice questions
- 1What gives a spacecraft the power to leave the earth?
- 2Who was the first Indian in space?
- 3In which year did he go to space?
- 4Which Indian mission went to the moon in 2008?
- 5Which Indian mission reached Mars in its first attempt?
- 6Name two uses of man-made satellites.
- 7What did Rakesh Sharma say when asked how India looked from space?
- 8Why is the earth called invaluable?
Show answers (try them yourself first)
- 1Rockets.
- 2Rakesh Sharma.
- 31984.
- 4Chandrayaan-1.
- 5Mangalyaan (M.O.M.).
- 6Weather forecasting and maps (also farming and telecommunication).
- 7"Saare Jahan Se Accha".
- 8No other planet with life has been found so far.
Quick revision
- Star = own light, twinkles; planet = no own light, no twinkle. Seven other planets besides the earth.
- Revolution = movement around the sun; orbit = path. Satellite, dwarf planet, asteroid.
- Gravity keeps things on the earth and planets in orbit. Rockets overcome gravity.
- Rakesh Sharma 1984; Chandrayaan-1 2008; Mangalyaan 2013-14.