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It is hard to determine the age of the Sun, because it won't change much over 100 million years or so. But what about the cosmic microwave background radiation, that is being mapped with ever better precision. It dates to only about 380 000 years after Big Bang. Is it possible to observe changes in it over a period of 10 years or 100 years, as it ages and cools, as the Hubble Bubble expands?

And how is the landscape of the CMB-map expected to change? Are relatively cool and hot areas permanent over time scale much larger than 380 000 years, or would our CMB-map be unrecognizable if we had lived, say, a billion years earlier or later?

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    $\begingroup$ @RobJeffries It certainly is! Sorry for not finding it myself, and thanks for finding it for me! $\endgroup$
    – LocalFluff
    Aug 1, 2019 at 6:33

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It isn't all that hard to determine the age of the sun, provided you are content with an accuracy of 100 million years or so either way. The radiometric dating of zircon crystals, which are only a little younger than the sun, gives a date of about 4.6 billion years, and it is generally agreed that the sun is about 5 billion years old. This is compatible with its position in the main sequence of a Hertzsprung-Russell diagram. You certainly wouldn't notice any change on the CMB map in a mere ten years, but a billion years hence it will have a noticeably greater red shift, except for the fact that there will be nobody here to notice or record it. Our descendants, every last one of them, will all have gone to meet their maker in far less than a billion years.

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  • $\begingroup$ Sure, for the Sun, then we can cheat by using geology and such. I was thinking of a Sun-like star in astronomical observations. $\endgroup$
    – LocalFluff
    Aug 12, 2019 at 11:04

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