Solar Astronomy: The Sun's Structure, Fusion and Wind

Our nearest star: the Sun

The Sun is the star at the centre of our Solar System: a giant ball of hot plasma that produces energy by nuclear fusion in its core and pours light and heat out into space. In this module you will learn how the Sun is built, how it makes its energy, and how the solar wind reaches all the way to the Earth.

Never look straight at the Sun

Looking directly at the Sun, especially through a telescope or binoculars, can cause permanent blindness. Astronomers observe the Sun safely in two main ways: - Projection: the telescope casts an image of the Sun onto a white card or screen. - An H-alpha filter: a special filter that passes only a narrow band of red light, revealing features such as prominences.

Inside the Sun

The Sun has layers, each with its own job:

From the centre outward

Put the Sun's regions in order, starting at the centre and moving out to the edge of the atmosphere.

• Core
• Radiative zone
• Convective zone
• Photosphere
• Chromosphere
• Corona

What each layer does

Where the Sun makes its energy

In which part of the Sun does nuclear fusion produce energy?

• The core
• The photosphere
• The corona
• The convective zone

Two ways energy travels out

Once energy is made in the core, it has a long journey to the surface, crossing two zones in different ways.

How fusion works

In the Sun's _____, hydrogen nuclei join together in a process called nuclear _____. They build up to form _____, and in doing so a tiny amount of _____ is converted into _____.

The Sun's outer atmosphere

Which layer is the Sun's faint outer atmosphere, seen streaming out during a total solar eclipse?

• The corona
• The core
• The photosphere
• The radiative zone

How fast does the Sun spin?

Astronomers track a sunspot across the Sun and find it moves about 13.3 degrees per day. A full rotation is 360 degrees. Estimate the Sun's rotation period, to the nearest day. (Hint: 360 divided by 13.3.)

The solar wind and Earth's shield

The Sun's hot corona constantly streams charged particles out into space. This flow is the solar wind. When it reaches the Earth, most of it is deflected by our planet's magnetic field, the magnetosphere. Some particles are trapped in doughnut-shaped regions called the Van Allen belts, and some funnel down towards the poles to create the aurorae.

Effects of the solar wind

The solar wind is a stream of charged particles from the Sun. Select the TWO effects it causes on or near the Earth.

• Aurorae, the northern and southern lights
• Geomagnetic storms that disrupt satellites and power grids
• Ocean tides that rise and fall twice a day
• The four seasons of the year

Spot the atmosphere

The Sun's atmosphere sits above the visible surface. Tap the TWO layers that make up the Sun's atmosphere.

• Chromosphere
• Core
• Corona
• Radiative zone
• Photosphere

Observe the Sun and stay safe

Make the safe, sensible choice in each situation.

• You want to show the Sun to a group using a telescope. What is the safe method?
• You want to see prominences and fine detail on the Sun. What should you use?
• A strong geomagnetic storm is forecast. What is a real effect operators prepare for?

Explain the Sun's energy

Explain how the Sun produces its energy and how that energy reaches the Earth. Write in clear, full sentences.

• Name the process in the core and the elements involved (hydrogen fusing into helium)
• Describe how energy moves out through the radiative zone and convective zone to the photosphere
• Explain what the solar wind is and one effect it has near the Earth
• Use the correct terms: fusion, photosphere, corona, solar wind