The Sun formed approximately 4.6 billion years ago from a collapsing cloud of gas and dust called the solar nebula. This nebula, composed primarily of hydrogen and helium with trace amounts of heavier elements, was part of a larger molecular cloud in the Milky Way galaxy. Gravity caused the nebula to contract and spin faster, eventually flattening into a disk. Most of the material was pulled towards the center, forming the Sun. As the center became denser and hotter, hydrogen fusion ignited, marking the birth of the Sun as a main-sequence star.