Stars and Galaxies

Stars are enormous balls of glowing gas, like our Sun. They look tiny only because they are incredibly far away from us. Deep inside every star, hydrogen is being squeezed and turned into helium in a process called nuclear fusion — and that is what makes a star shine so brightly.

Why do stars seem to twinkle? It is not the stars themselves — it is our air. As starlight passes through Earth's moving atmosphere, the light gets bent this way and that, making the star appear to shimmer. Above the atmosphere, in space, stars shine with a steady, unblinking light.

Stars come in different colours, and the colour tells us how hot a star is. The hottest stars glow blue-white, medium stars like our Sun shine yellow, and the coolest stars glow red or orange. This is the opposite of what many people expect — blue is hotter than red!

Stars do not last forever. They are born inside huge clouds of gas and dust called nebulae, they shine for millions or billions of years, and eventually they run out of fuel. Small stars fade away quietly, but the biggest stars end in a gigantic explosion called a supernova.

Stars gather together in huge groups called galaxies. Our galaxy is the Milky Way, and it contains hundreds of billions of stars. And there are billions of other galaxies too! When you gaze at the night sky with your eyes alone, almost every point of light you see is a star inside our own Milky Way.