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What if the Earth could be moved away from the Sun when it becomes a red giant

  1. Nov 25, 2007 #1
    If we could move the Earth, how far away from the Sun would it need to be to maintain a temperature similar to what we have now when it becomes a red giant?

    How large would the Sun apear in the sky?

    Would the sky still be blue?

    Would everything have a red tint to it?

    I was thinking about this on the way to work today. I think it would make a nice picture to show the Earth's landscape with a huge red star in the sky. I'm learning 3dstudio and this is something I may try. I would like to have some accuracy though instead of just guessing.
  2. jcsd
  3. Nov 25, 2007 #2


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    You could calculate the distance by comparing the current temperature of the sun to the new temperature and applying the Stefan-Boltzman equation to find the new distance required to keep the solar flux the same. What you will find is that the sun would appear larger in the sky (it would be cooler, so it must appear larger to send us the same amount of energy).
  4. Nov 26, 2007 #3


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    Would the change in frequency that makes the Sun red prevent photosynthesis?
  5. Nov 26, 2007 #4
    Would it be easier to deliberately adjust the Earth's orbit, or make plants that don't care? :rolleyes:
  6. Nov 26, 2007 #5
    Some quick notes-

    1.) The Sun going supernova isn't on the list at all, because the sun doesn't have the mass to pull it off.

    2.) There's the philosophical idea that sense we've become sentient and able to manipulate our enviroment natural selection and evolution won't work the same way for us. As our ability to manipulate our surrondings improves natural selection will become less prominient, and possibly reaching the point where we can define our own evolutionary path.

    I for one like to imagine a day 5 billion years in the future when what humanity has become parks on Mars and watches as the Sun swallows the Earth, raises a toast for our home planet, then moves along it's merry way.
  7. Nov 26, 2007 #6


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    I'm more of an optimist, Chris. Technologically capable intelligience has huge survival value, providing we refrain from using it to exterminate ourselves. We can colonize other planets - something no other critter on earth do [save perhaps for the hardiest of microscopic life forms]. Moving earth might be a daunting task, but migrating to mars or a space platform platform appears very doable. If our technologically continues to evolve for another 4 billion years, this will surely look like a high school science project. In fact, there are any number of other species [e.g., cetaceans, parrots, octupi, apes] that may be sufficiently evolved to accomplish this feat in that amount of time.
  8. Nov 27, 2007 #7
    Wasn't there a Doctor Who episode that revealed that Trees did exactly that?
  9. Nov 27, 2007 #8
    Hmm. Photosynthesis from a red giant (or any other wavelength for that matter) would probably favor a species that could absorb specific wavelengths of light that are specifically attuned to it's particular wavelengths. You'd probably see life adapt to it over time, and the colors of plants would adapt as well. Purple grass? It is an Interesting thought, even if it is not all that "practical" of a question in the short term. :)
  10. Nov 27, 2007 #9
    My guess it that no only will microcrobes have beaten us to the various planets by billions of years in many cases, they'll outlive us as well. :) Besides, even if we found an empty planet while cruising around in space, I don't think we'd be very happy without some plant life around, if only for the decoration and some corn on the cob and a nice cold beer once in a while. :)
  11. Nov 27, 2007 #10
    Have you ever thought of a scenario that some kinds of microbes could evolve to the extent that they survived in the new extremely severe conditions: no air, too, too hot or too cold and then by certain reasons, they moved to Mars or Europa etc.. New life could start out there.
  12. Nov 27, 2007 #11


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    How quickly does a sun-like star leave the main sequence? Will the Sun expand into a red giant gradually over the course of millions of years (still a blink of the eye in stellar timescales), or is it a quick process taking perhaps minutes to days?

    I imagine the Sun would still be very bright over the entire visible spectrum, so plants should still be able to perform photosynthesis. As it is now, plants have many pigments to take advantage of different wavelengths of sunlight. If the Sun gradually expanded, allowing us time to gradually move its orbit, I imagine that plants would quickly evolve to the new light.

    We've already performed a similar experiment when we take plants indoors where they must receive light through glass and plastic. That must change the spectrum to some degree, yet houseplants do quite well.
  13. Nov 27, 2007 #12


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    Here's an image that shows the time scale of the Sun's evolution. Note that the Sun gradually warms over billions of years before expansion to Red Giant, the expansion can take 100's of millions of years.

  14. Nov 27, 2007 #13


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    Thanks for the link. The image doesn't make this obvious. At 9 billion years it's still main sequence, and at 10 billion years it's a red giant. But the transition is not shown. Did it slowly grow from its diameter @9Gy to its diameter @10Gy? Or did it happen all of a sudden one day inbetween 9 & 10 Gy? If this graph had higher resolution, what would the Suns at 9.1, 9.2,...9.9 look like? Would they be growing in diameter, or would there still be a sudden jump from a small yellow star to a big red star?

    I suspect you're right, that the transition can take hundreds of millions of years.
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