The Sun

The Sun is a star: the star closest to us. It is an extremely hot, round ball of gases. It gives out a huge amount of energy, which is why it glows so brightly. (A book, a planet or the Moon gives no light of its own; they shine only when light falls on them.)

The Sun's heat keeps the Earth at a temperature where life is possible. Plants need sunlight to grow, and plants give food and oxygen to animals, including us. The Sun is also responsible for climate, seasons, weather, the water cycle and winds.

How big is it? The Sun is about 100 times wider than the Earth. It looks small because it is very far away: about 150 million km. This distance is used as a unit for distances in the Solar System, called the astronomical unit (au). So the Earth is about 1 au from the Sun.

The other stars are much, much farther away. The nearest star after the Sun, Proxima Centauri, is about 269,000 au away. That is why the Sun looks so much bigger and brighter than other stars, and why stars look like tiny points, even though some are much bigger than our Sun. In the daytime we cannot see the other stars at all: they are still shining, but the Sun is far too bright.