Download Astrophysics

2. Our favourite star
The Sun photographed in soft X-rays
The Sun’s stats
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Distance:
Radius:
Mass:
Average density:
Surface temperature:
Luminosity:
1 AU=150 million km
700,000 km
2 x 1030 kg
1.4 kg/litre
5,800 K
3.9 x 1026 watts .
It gives us life and energy
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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!
Atkinson, 1920: The Sun’s energy comes from
the fusion of hydrogen nuclei to helium
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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
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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.
Our insight into the workings of
the Sun enables us to understand
the stars better …