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Asked by anon-334456 on 23 Sep 2022.
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Jack Reid answered on 23 Sep 2022:
Over time, the Sun has been variable. Its magnetic field has grown stronger and weaker over centuries. As a result, its energetic output has varied, with it sometimes hotter and sometimes cooler, because the magnetic field controls so much of what happens with the Sun. This can affect us on Earth: centuries ago, when the Sun was quite quiet and the magnetic field weaker, the Earth was cooler, and the Thames froze over!
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Mike Heyns answered on 24 Sep 2022:
On the seriously long timescales, the Sun has got progressively hotter since its birth nearly 5 billion years ago. As the nuclear fusion reactions in its core keep going, the surface temperature and luminosity will continue to increase, and even accelerate. There will come a point where most of the fuel is used up and the Sun will expand in size to become a red giant, still brighter but with a cooler surface temperature (due to their massive size).
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