How Big is the Sun?The Sun is about 1,391,980 kilometres (864,938 miles) in diameter. This is a size that is almost difficult to imagine. In comparison, your planet Earth is only 12,756 kilometres (7,926 miles) wide, and even Jupiter, the biggest planet in the solar system, is only 142,600 kilometres (88,700 miles) wide. The picture below will help you to imagine the size of the Sun compared with the size of Earth and Jupiter. The Sun contains over 99% of the matter in the Solar System. The rest of this matter is taken up by the planets, comets, asteroids and moons of the solar system.
The Sun is huge, but is tiny in comparison to some other stars. Older stars, such as a star called Betelguese, are 500,000,000 kilometres wide, 500 times bigger than the sun! As stars get older, they get bigger. Our star, the Sun, is about 4.5 billion years old, only half way through its life. When it gets older, it will become bigger and "eat up" some of the inner planets, Mercury, Venus, and possibly Earth and Mars. It is unlikely that people will still exist on Earth though by the time this happens.