Schematic illustration showing the development of the Universe from the Big Bang to the present day. At the centre is the Big Bang itself, the event that created space and time and began the Universe's expansion. After 380, 000 years, the Universe became opaque to radiation for the first time, and matter began to clump together to form gas clouds. By 200 million years, localised gravitational contractions within these gas clouds had led to the first generations of stars. Then the first galaxies are thought to have developed after around 1 billion years. The Solar System (bottom right) originated around 9 billion years after the Big Bang. And lastly, today, 13.8 billion years after the Big Bang, the Universe is still expanding and, it is thought, accelerating as it does so. |