2. Our favourite star

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2. Our favourite star
The Sun photographed in soft X-rays
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The Suns stats

• Distance 1 AU150 million km
• Radius 700,000 km
• Mass 2 x 1030 kg
• Average density 1.4 kg/litre
• Surface temperature 5,800 K
• Luminosity 3.9 x 1026 watts .

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It gives us life and energy

• Humans have always revered the Sun
• But where did it get its energy from?
• If it were coal it would only last 10,000 years!

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Atkinson, 1920 The Suns energy comes from the
fusion of hydrogen nuclei to helium

• The forces between nucleons are about 100,000,000
  times as strong as those between atoms.

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• This means that the energy involved in nuclear
  reactions will be hundreds of millions times
  greater than that involved in chemical reactions
• The Sun would last nearly 100 billion years on
  its hydrogen fuel but other processes will
  cause problems before then!

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• We now know a lot about how the Sun works from
  computer models based on the laws of physics.

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• The corona, the source of the solar wind becomes
  visible in an eclipse.

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• The solar wind brings us auroras.

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• Sunspots are the result of knots in the
  magnetic field of the Sun. They untie every 11
  years.

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Our insight into the workings of the Sun enables
us to understand the stars better