Humans have always been fascinated by the heavens. Cycles on Earth were recognised as being linked with changes in the heavens very early in human history.
From the beginning of time there have been many attempts to explain how the universe came into being. As our instruments for the exploration of the universe have become more sophisticated, we have learned much. The most popular theory at the present time is the "Big Bang" Theory, or a variant, which proposes that the universe started with a massive explosion. Here are some links to sites explaining the theory