Most of the time the Sun is quiet, shining in space beaming out light and heat. But every eleven years it gets cranky – covered in dark spots and fiery eruptions. This is a time called solar maximum, or solar max for short.
The Sun, like all stars, is a big ball of plasma – mostly hydrogen and helium. Because the Sun is so big – 100 million times bigger than Earth – it has a lot of gravity. The gravity squeezes the plasma so hard that it gives off heat and light. Scientists call this nuclear fusion.
Twenty years ago, the answer this question was ‘only one that we know’. Most astronomers believed that the Sun was no different to most stars in the universe. So if we had a star with planets and moons – a solar system – than why don’t others.
This is a difficult question to answer, because the number keep growing.
