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Physics · Space physics

Our solar system

Describe the structure of the solar system, the formation of the Sun and planets, and the orbits of planets, moons and artificial satellites (Physics only).

  • 6 key terms
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Teacher resources

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Student handouts

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Warm-up

Answer each one, then check.

  1. 1

    What force holds planets in orbit?

    Show answerHide answer

    Gravity

  2. 2

    Name the star at the centre of our solar system.

    Show answerHide answer

    The Sun

  3. 3

    Name the galaxy we live in.

    Show answerHide answer

    The Milky Way

  4. 4

    Name three planets.

    Show answerHide answer

    For example Earth, Mars and Jupiter

  5. 5

    What is a moon?

    Show answerHide answer

    A natural satellite of a planet

Learning Objectives

  1. 1Describe the structure of the solar system and our galaxy.
  2. 2Describe how the Sun and the planets formed.
  3. 3Describe the orbits of planets, moons and satellites.
  4. 4Describe the force that keeps an object in orbit.
  5. 5Explain the difference between natural and artificial satellites.

THE SOLAR SYSTEM

Our solar system is made up of the Sun at the centre, eight planets, dwarf planets, moons, asteroids and comets. It is part of the Milky Way galaxy. Gravity causes objects to orbit.

Our Sun is one of about 100 billion stars in the Milky Way galaxy.

How the Solar System Formed

Follow the steps.

  1. 1 A nebula

    A huge cloud of dust and gas collapses under gravity.
  2. 2 Protostar

    Gravity pulls the gas together. It gets hot and dense.
  3. 3 A star is born

    Nuclear fusion begins; the Sun starts to shine.
  4. 4 Planets

    Material left over clumps together to form planets and moons.

Orbits

Learn what orbits what.

  • Planets

    Orbits: The Sun. Type: Natural

  • Moons

    Orbits: A planet. Type: Natural satellites

  • Weather and communications satellites

    Orbits: The Earth. Type: Artificial satellites

  • Comets

    Orbits: The Sun. Type: Elliptical orbits

Orbits and Gravity

Explain why the Moon stays in orbit around the Earth.

Show the solutionHide the solution
  1. 1 Gravity The Earth's gravity pulls the Moon towards it
  2. 2 Centripetal force Gravity is the force towards the centre of the orbit
  3. 3 Result The Moon keeps changing direction so it follows a circular path

AnswerGravity acts as the force towards the centre.

Key Facts

Learn these.

  • Planets

    Eight; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

  • Galaxy

    A huge collection of billions of stars, like the Milky Way.

  • Dwarf planets

    Small bodies that orbit the Sun but have not cleared their path, such as Pluto.

  • Comets

    Icy bodies on very elliptical orbits round the Sun.

Solar Order

Put the planets in order from the Sun. Make a mnemonic. Then state which are rocky and which are gas giants.

1. Inner four rocky, outer four giants.

A good answer shows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The first four are rocky; Jupiter and Saturn are gas giants; Uranus and Neptune are ice giants.

Can I...?

  1. 1Describe the solar system.
  2. 2Name the eight planets.
  3. 3Define a galaxy.
  4. 4Describe how a star forms.
  5. 5Describe how planets form.
  6. 6Name natural satellites.
  7. 7Name artificial satellites.
  8. 8Say what keeps orbits going.

Summary & Exam Focus

  • Sun, eight planets, moons, asteroids and comets.
  • Gravity pulls a cloud of dust and gas together to form the Sun.
  • Moons are natural satellites; weather satellites are artificial.
  • Gravity is the force towards the centre of an orbit.

Exam focus

Name the force that keeps the planets in orbit round the Sun. (1 mark) (1 marks)

Gravity.

Key terms

The vocabulary this lesson expects you to use. Each one is linked from the first place it appears above.

Solar system
The Sun and all the objects that orbit it.
Galaxy
A huge group of billions of stars held together by gravity.
Natural satellite
A moon that orbits a planet.
Artificial satellite
A human-made object that orbits a planet.
Nebula
A cloud of gas and dust in space.
Orbit
The curved path of an object round another because of gravity.

Questions and answers

10 questions set on this lesson, with the mark schemes and model answers open.

1. Exam question State 2 marks Easier

Name the galaxy that contains our solar system and state what holds the galaxy together.

Mark scheme — 2 marks available

  • Milky Way — 1 mark
  • Gravity — 1 mark

Model answer

The Milky Way. Gravity.

2. Exam question Describe 3 marks Easier

Describe how the Sun and the planets in our solar system were formed.

Mark scheme — 3 marks available

  • Gravity pulls dust and gas together — 1 mark
  • Fusion starts forming the Sun — 1 mark
  • Planets form from the remaining material — 1 mark

Model answer

A cloud of dust and gas (nebula) was pulled together by gravity. It became hot and dense and nuclear fusion began, forming the Sun. Material left over in orbit clumped together under gravity to form the planets.

3. Exam question State 2 marks Easier

Give one example of a natural satellite and one example of an artificial satellite.

Mark scheme — 2 marks available

  • Natural satellite — 1 mark
  • Artificial satellite — 1 mark

Model answer

Natural: the Moon (or any moon). Artificial: a weather, communications or GPS satellite.

4. Exam question Explain 3 marks Easier

Explain why the Moon stays in orbit around the Earth.

Mark scheme — 3 marks available

  • Gravitational attraction between Earth and Moon — 1 mark
  • Force is towards the centre of the orbit — 1 mark
  • Changes direction so a curved path is followed — 1 mark

Model answer

The Earth's gravity pulls the Moon towards the Earth. This force is always towards the centre of the orbit and continually changes the direction of the Moon's velocity, so it follows a curved path.

5. Exam question Explain 3 marks Easier

Explain why the outer planets take longer to orbit the Sun than the inner planets.

Mark scheme — 3 marks available

  • Longer orbit or further distance — 1 mark
  • Weaker gravity further away — 1 mark
  • Lower orbital speed — 1 mark

Model answer

The outer planets are further from the Sun, so they travel a longer orbit. Gravity is weaker further away, so they also move more slowly.

6. Multiple choice 1 mark Easier

The Earth orbits the...

  1. A Moon
  2. B Sun Correct
  3. C Milky Way
  4. D Mars

Why: It is a planet.

7. Multiple choice 1 mark Core

Our galaxy is called the...

  1. A Andromeda
  2. B Solar System
  3. C Milky Way Correct
  4. D Big Bang

Why: The Milky Way.

8. Multiple choice 1 mark Core

A natural satellite is a...

  1. A planet
  2. B star
  3. C comet
  4. D moon Correct

Why: It orbits a planet.

9. Multiple choice 1 mark Core

What forms planets from leftover material?

  1. A gravity Correct
  2. B magnetism
  3. C friction
  4. D sound

Why: It pulls material together.

10. Multiple choice 1 mark Stretch

Planets are held in orbit by...

  1. A friction
  2. B gravity Correct
  3. C magnetism
  4. D the Moon

Why: Gravity pulls them to the Sun.