What is going to happen to the sun in 1 billion years from now?

In about 1 billion years, the Sun is expected to increase in brightness and heat, which will significantly affect Earth's climate and atmosphere. This intensified solar output could lead to the evaporation of oceans and make the planet uninhabitable for most forms of life. Eventually, the Sun will transition into its red giant phase in about 5 billion years, expanding and possibly engulfing the inner planets, including Earth.