Answer to Vekseid's question:http://www.dawn.com/2002/04/06/int17.htm
Simple answer, the earths orbit will not stay the same. As the sun swells it will continue to lose surface mass,
The pertinent results are these. In about 7.5bn years, the solar radius will grow to about 167m kms (compared to the present 0.7m). If the Earth remained at its present distance it would be enveloped, but a gradual migration to 185m kms will have occurred due to the solar mass loss.
That is the first red giant phase. Itís interesting to note that while the Earth will remain outside the sun, the latter will fill about half the sky.
The sun will then shrink before again fattening about 120m years later. In that epoch its radius will maximize at 172m kms, but our planet will have shifted outwards to 220m. The closest call is therefore in the first instance.
this is a copy paste, I am trusting this site's equations and mathematical calculations. I am Lazy.
A new Question to come.