How do astronomers think the universe was created?

Most astronomers think that the Universe was formed during an event called the Big Bang - a giant explosion which occurred between 10 and 20 billion years ago. During the Big Bang, all of the space, time, matter, and energy in the Universe was created. This giant explosion hurled matter in all directions and caused space itself to expand. As the Universe cooled, the material in it combined to form galaxies, stars, and planets.