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How big will the sun get when the seas begin to boil?

  1. Feb 19, 2012 #1
    First of all, I apologize if this is not the right place - it's my first post (although I've lurked for a while), so... er.

    Doomsday question. I'd like to know how big the sun will get - visually (but please without °, I am not educated enough to understand those) - at the end of its life cycle at the moment when the seas on Earth begin to boil. And also how bright and what color the light will be, if possible.
  2. jcsd
  3. Feb 19, 2012 #2


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    After some poking around, here's what I came up with as a rough estimate. In about 3.6 billion yrs the Sun will have slowly increased its output by ~40%, the seas will evaporate and Earth becomes another Venus. The radius of the Sun will have increased by ~18%. Its color will not appreciably changed.
  4. Feb 19, 2012 #3
    Thank you very much. Although, that's not much potential for drama, is it?:smile:
  5. Feb 19, 2012 #4


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    No, but at that point in time the Sun will not be a Red Giant yet. That will happen at approximately 5 billion years from now. It is expected that the diameter of the Sun will be 2 au, which means its radius will be about 1 au, so it will extend out to Earth's current orbit.

    The apparent size of the Sun will increase from about 0.5 degrees (the apparent size that it is now) to about 90 degrees, an increase of over 200 times. So it will appear about 200 times as big as it does now.

    Now that is assuming the Earth is still near 1 au from the center of the Sun. If we assume the Earth will get further away over time as the Sun loses mass, the Sun will appear slightly smaller.
  6. Feb 19, 2012 #5


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    His last statement suggested to me that he's writing a story. The end of life on Earth will come when the oceans dry up - loooong before the sun starts doing anything more ... dramatic.
  7. Feb 19, 2012 #6


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    Hrmm. I could have swore I saw "Red Giant" somewhere in the post...my apologies.
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