The Sun – Lesson Summary

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Learning Objective

In this lesson we will learn about the different parts of the Sun and the processes they are characterised by. We will also discuss how the Sun influences life on Earth.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe the Sun’s physical and chemical characteristics.
  • Explain how the Sun produces energy.
  • Describe the three main layers of the Sun’s interior.
  • Describe the three main layers of the Sun’s atmosphere.
  • Describe the solar cycle.
  • Describe sunspots, solar flares, coronal mass ejections, prominences and solar wind.
  • Discuss how the Sun influences Earth.

 
the sun online science lesson contents

(Image: NASA/Goddard/SDO)

Lesson Topics

1 | Our Sun

2 | The Sun’s Physical and Chemical Properties

3 | Energy From the Sun

4 | The Solar Interior

5 | The Solar Atmosphere

6 | Solar Wind and the Auroras

7 | The Sun’s Magnetic Field and Solar Activity

8 | Earth, Sun and Moon

9 | Summary

Lesson Summary

  • The Sun is a medium-sized star at the centre of our solar system.
  • Planets, moons, comets and asteroids orbit the Sun under the influence of its gravity.
  • Without the Sun’s heat and light, there would be no life on Earth.
  • The Sun is 1.3 million times the size of Earth and 330,000 times the mass.
  • The Sun rotates on its axis every 26-35 days and its axis is tilted by 7.25 degrees.
  • The Sun is about three quarters hydrogen and one quarter helium, with a small amount of other elements.
  • Matter within the Sun exists primarily as plasma, which is super-heated, ionised gas.
  • The Sun’s energy comes from the nuclear fusion of hydrogen into helium.
  • This reaction produces enormous amounts of light and heat, as well as other types of electromagnetic radiation.
  • The solar interior consists of three main layers:
  • The core – the extremely hot and dense inner region of the Sun, where nuclear fusion occurs.
  • The radiative zone – the middle layer of the Sun’s interior, which is characterised by the transfer of energy by radiation.
  • The convective zone – the outer layer of the Sun’s interior, which is characterised by the transfer of energy by convection.
  • Temperature and density of the solar interior both increase greatly with depth.
  • The solar atmosphere consists of four main layers:
  • The photosphere – the lower layer of the Sun’s atmosphere, which emits the light we see on Earth.
  • The chromosphere – the middle layer of the Sun’s atmosphere, which emits a faint reddish glow.
  • The transition region – a thin layer where temperature increases dramatically.
  • The corona – the upper layer of the Sun’s atmosphere, which is composed of whitish streams and loops of ionised gas.
  • Temperature decreases in the photosphere, then increases greatly in the chromosphere and corona.
  • Matter from the corona continually blows away, forming solar wind.
  • When solar wind reach Earth, it is creates the auroras.
  • The Sun has a magnetic field that fluctuates over an 11 year cycle known as the solar cycle.
  • These fluctuations generate solar activity, including:
  • Sunspots – dark, circular regions on the Sun’s surface that are much cooler than surrounding areas.
  • Solar flares – enormous surface explosions that are sometime accompanied by coronal mass ejections, which are massive expulsions of highly energised plasma.
  • Prominences – glowing streams of plasma that often form a loop and extend for thousands of kilometres.
  • Besides providing the heat and light that sustains life, other phenomena on Earth that are influenced by the Sun include:
  • Day and night.
  • The seasons.
  • Weather and climate.
  • Phases of the Moon.
  • Eclipses
  • Tides.
  • Auroras.

 
solar prominence and solar flare

Size of a solar prominence and solar flare relative to Earth.

(Image: NASA/SDO/GSFC)

(Header image: NASA/SDO)