Cosmic expansion refers to the phenomenon where the universe is continuously growing larger over time. This process was first observed by astronomer Edwin Hubble in the 1920s, who discovered that distant galaxies are moving away from us, indicating that the universe is expanding. The farther away a galaxy is, the faster it appears to be receding, a relationship known as Hubble's Law. The expansion of the universe began with the Big Bang, approximately 13.8 billion years ago. As the universe expands, it cools, allowing matter to form stars, galaxies, and other cosmic structures. This ongoing expansion is a fundamental aspect of modern cosmology and helps scientists understand the universe's history and future.