How long would it take the sun to swallow the earth?

Answer 1

This may or may not happen, but if it does happen it will be in about 4 billion years.

This is because by then, the Sun will have fused a substantial part of its hydrogen nuclear fuel, and the helium "ash" that's left behind after the hydrogen fusion will begin to interfere with the hydrogen fusion. The Sun will begin to contract.

This contraction, under the force of its own gravity, will cause the Sun's core to heat up and the pressure will increase. At some point, the temperature and pressure will become high enough so that the helium "ash" will begin to fuse into heavier elements such as oxygen and carbon.

This new heat and energy will cause the Sun to expand again, this time into a red giant. Mercury and Venus will almost certainly be consumed at this time, but scientists are uncertain if it will expand enough to swallow the Earth.

If the Earth is still in its present orbit, it will be incinerated even if it isn't consumed. However, if humanity survives, we will surely know how to tow the Earth out from the Sun, and perhaps place it in orbit around Jupiter. (We already know_HOW_; we just can't DO it yet.)