| MadSci Network: Astronomy |
If the Sun ever got close to the Earth, we would be in serious trouble! It wouldn't take too much heat before a runaway greenhouse would make the Earth uninhabitable. That's basically what happened on Venus, where the surface temperature is 750 degrees (hot enough to melt lead!).
Fortunately, the orbit of the Earth around the Sun is very stable. It would take a severe, and very unlikely interaction with the other planets to change the Earth's orbit enough to bring us too close to the Sun. We can predict the orbits of the planets well enough to say that an interaction will certainly not happen for millions of years, and will probably never happen.