A red giant is a kind of star that represents an evolutionary phase of intermediate and high-mass stars that have surpassed their main-sequence lifetimes. When a star like the Sun becomes a red giant, a sudden burst of energy is produced by new fusion processes at the core of the star. This burst pushes the plasma in the star outward. When the equilibrium of the star’s inward and outward forces are restored, the star has swelled to about one hundred times its original diameter. The swollen, bloated star is so large that its outer layers do not contain as much star-stuff, and the star’s surface (photosphere) cools down to the temperatures of red dwarfs (about 6,000 degrees Fahrenheit or 3,000 kelvin). The Sun is destined to become a red giant, and when it does, about five billion years from now, it will swallow the planets Mercury and Venus, and destroy Earth as well.