At this point, the Sun will have run out of hydrogen and the forces of gravity towards the inside of the star will overcome the external pressures acting on the star.
As a result, the Sun will begin to expand and cool like an inflated balloon.
NASA estimates that the red giant will be about 2,000 times brighter than the current Sun.
But even more troubling, the expanding star is likely to envelop the innermost planets, Mercury and Venus.
And while the Earth could stay out of the reach of the red giant, its heat will be strong enough to burn the planet.