Question: When will the sun explode?

Tim Duckenfield answered on 5 Mar 2018:

The Sun is roughly middle aged, having been around for ~4.5 billion years, and we think it will continue for about ~4 to 5 billion more. When it gets to the end of its life, the fuel the Sun is ‘burning’ will get close to running out (not really burning, actually nuclear fusion which is far more dramatic!). The weight of the Sun will cause it to contract and shrink, as all the gas crushes down. Then the Sun ‘explodes’, but not in a dramatic supernova that will outshine a galaxy – our Sun is a bit small for that. Really that shrinking brings all the last bits of fuel together so they fuse for a bit longer – but enough to push out all the gas again to form a “red giant”. These are big but cool stars, for example think about how ‘white-hot’ is hotter than ‘red hot’. The Sun when it becomes a red giant will grow to reach beyond the orbit of Mercury, maybe even as far as Earth!!! So very very big. Then it will stay a red giant for about 1 billion years, cooling and shrinking until it throws off its cold outer layers in another mini-explosion, to leave behind a ‘white dwarf’ star from what was left of our Sun’s core.