Filling the frame with its baleful glare is a red giant star, the final World Of Wonder in my JSVB series. And, as it happens, it will likely be our Earth's final world of wonder as well.
Roughly five billion years from now, our yellow sun will retire from being relatively small and yellow, consume the last of its ordinary hydrogen supply, and then expand massively as increasing core heat allows for another, hotter round of hydrogen fusion. At the end of expansion, the sun will cool and turn red.
Expansion: that's the trick. The Sun will in time expand to at least the orbit of the Earth and probably beyond that of Mars. A billion years prior, the heat of the initial stellar expansion will have burnt away our atmosphere, so there's not much reason to stick around for the big sundive after that.
Just so you know, there is an active international consortium working through ideas to save the Earth from being consumed by the Sun. The most effective plan will be to mount engines on the Moon and gradually de-orbit it from Earth. Then, we aim the Moon at the Sun in a slingshot trajectory. The Moon will come back to us accelerated by the gravity well of the Sun. Careful aiming will have the Moon brush by just close enough to wobble Earth's orbit and pull it fractionally away from the sun. The trick is to create a pull that doesn't cause massive tidal damage. Then, the Moon will swing away into the outer Solar System before returning for another slingshot run, one terrestrial pass every hundred years or so.
After a few thousand years of these cosmic nudges, the Earth's orbit may widen enough for us to find the new habitable zone past Mars or Jupiter, or we may break our planet free altogether and drift in deep space as one of an innumerable cast of runaway rogue planets, sunless and hurtling through the uncharted galaxy.
We have to get past the year 2014, though, before we can worry about saving Earth.
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