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Basic 6 · Science · Earth Science

The Relative Sizes of the Earth and the Sun

In this topic you will describe the relative sizes of the earth and the sun and explain why the sun is important.

By the end of these notes you should be able to:

  • Compare the sizes of the earth and the sun
  • Explain why the sun looks small from the earth
  • Describe the importance of the sun to the earth

What you already know

  • Benefits of the sun (Basic 5)

Copy everything that has a blue line on its left into your notebook. The other parts are for reading.

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Earth Science
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B6.2.1.1.1 – Describe the relative sizes of the earth and sun and their importance

Introduction

From the earth, the sun looks like a small, bright ball in the sky. In fact, the sun is enormous. More than a million earths could fit inside it.

1. How Big Is the Sun?

Earth and sun compared
FeatureEarthSun
typeplanetstar
diameterabout 12,700 kmabout 1,390,000 km (about 109 times wider)
volume1 earthabout 1.3 million earths could fit inside
surface temperatureabout 15 °C on averageabout 5,500 °C
lightdoes not make its own lightgives out its own light and heat
The sun drawn as a huge circle with a tiny earth beside it
Figure 1: Relative sizes of the sun and the earth Draw a large circle (sun) and a tiny dot (earth) to show their sizes.Illustration: Sirbus

2. Why Does the Sun Look Small?

The sun looks small because it is very far away, about 150 million kilometres from the earth. Light from the sun takes about 8 minutes and 20 seconds to reach us. Objects look smaller the farther away they are, just as an aeroplane high in the sky looks tiny even though it is very big.

3. A Model of the Sizes

If the earth were the size of a peppercorn (about 2 mm across), the sun would be the size of a large football (about 22 cm across), placed about 23 metres away. This model shows both the huge size difference and the great distance.

The moon looks about the same size as the sun in the sky, but the sun is about 400 times wider. It only looks similar because it is also about 400 times farther away.

4. Importance of the Sun

  • Gives light and heat; without it the earth would be dark and frozen.
  • Provides energy for photosynthesis, so all food chains depend on it.
  • Drives the water cycle by evaporating water.
  • Causes winds and weather by heating the earth unevenly.
  • Its gravity keeps the earth in orbit, giving us years and seasons.
  • Provides solar energy for electricity and drying crops.

Safety: Never look directly at the sun, even during an eclipse. It can damage your eyes permanently.

New words

star
A huge ball of hot gas that gives out light.
planet
A large body that orbits a star.
diameter
The distance across a circle through its centre.
relative size
Size compared with something else.
orbit
The path of one body around another.
gravity
The force that pulls objects towards each other.

Summary

  • The sun is a star about 109 times wider than the earth.
  • About 1.3 million earths could fit inside the sun.
  • The sun looks small because it is about 150 million km away.
  • The sun gives light, heat and energy for life on earth.

Class activity: Scale Model

  1. Use a peppercorn (earth) and a football (sun).
  2. Measure 23 large steps across the field to place them.
  3. Discuss what the model shows about size and distance.

You need: Locally made clay globe, Torch, Printed day-and-night picture cards

Exercises

Answer in your exercise book first, then check your answers.

  1. 1. Which is bigger?

    • A. The sun
    • B. The earth
    • C. They are equal
    • D. The moon
    Show answer
    Answer: The sunIt is a huge star.

  2. 2. About how many earths could fit inside the sun?

    • A. 1.3 million
    • B. 10
    • C. 100
    • D. 1,000
    Show answer
    Answer: 1.3 millionIts volume is enormous.

  3. 3. Why does the sun look small?

    • A. It is very far away
    • B. It is tiny
    • C. It is cold
    • D. It is behind clouds
    Show answer
    Answer: It is very far awayAbout 150 million km.

  4. 4. The sun is a star.

    • A. True
    • B. False
    Show answer
    Answer: TrueIt gives its own light.

  5. 5. Sunlight reaches the earth instantly.

    • A. True
    • B. False
    Show answer
    Answer: FalseIt takes about 8 minutes 20 seconds.

  6. 6. The sun's diameter is about ______ times the earth's.

    Show answer
    Answer: 109About 109 times.

  7. 7. State three ways the sun is important to the earth.

    Show answer
    Answer: Gives light and heat, provides energy for plants, drives the water cycle.Any three.

  8. 8. Explain why an aeroplane high in the sky helps us understand the size of the sun.

    Show answer
    Answer: Both look small because they are far away, even though they are actually very big.Distance affects apparent size.

Homework

  1. Make a poster showing the sizes of the sun and earth with three facts.