When will the sun stop shining?
In about five billion years.
The sun, like every star in the universe, is nothing but a huge ball of gas. It’s about 1.5 million kilometres in diameter. It’s in a constant fight against its own weight—it weighs 2,000,000,000,000,000,000,000,000,000,000 kilograms (2 times 10 to the 30 kilograms).
The only thing that stops it collapsing into itself under its own weight is nuclear fusion—which keeps it inflated like a balloon. The energy produced gives us sunlight and heat and generally keeps us alive.
The sun fuses a minimum of 4 million tonnes of hydrogen every second. It will exhaust itself and eventually collapse in five billion years from now—that will be the end of the sun as we know it.