☀ How stars shine

A star is a giant ball of hot gas held together by its own gravity. In its core the pressure is so high that hydrogen atoms fuse into helium, and a little mass turns into a lot of energy (Einstein's E = mc²).

• The Sun turns about 4 million tonnes of matter into energy every second.
• Light made in the core takes thousands of years to reach the surface — then just 8 minutes to reach Earth.
• The Sun is about 4.6 billion years old and halfway through its life.