Looking into the past
Like everything else, light takes time to travel across space. Light from the moon takes just over a second to reach us, and light from the Sun about eight minutes. When you look into the sky, then you are not seeing the present but the past - a wave of light that may have set out several thousand years ago. Our ability to look into the past is limited by our eyesight. But with modern telescopes, which can pick up not only light waves but also X-rays and radio wave, we can see even farther back - more than 10 billion years. In 1964, two American scientists detected a microwave 'hiss' coming from all directions of the sky. They realised that this hiss must be radiation released in the Big Bang still echoing throughout the Universe.

A mocrowave map of the sky, compiled from data gathered by satelite, glows with light created when the Universe began.

Universe now
Today, clusters of stars form different shaped galaxies. The heat of the Big Bang has dwindled to a faint background radiation.

Big Bang
During the Big Bang, the fireball flies apart, expanding rapidly and then cooling to form the first atoms - the simplest ones within three minutes, more complex ones taking 500 000 years.

Star birth
In the first billion years or so, clouds of atoms of hydrogen and helium gas thicken into the beginnings of galaxies and stars.