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The Sun was born a little over 4.5 billion years ago from a ten-kelvin interstellar cloud, roughly 1014 kilometers across, of cold atomic and molecular gas. Triggered by an event like a nearby supernova, supersonic turbulence in the cloud caused a compressed region to collapse under its own gravity, fragmenting into smaller (on the order of 1012 kilometers) pieces on a timescale of about two million years. These clumps flattened into disks from their angular momenta, feeding the disk centers as they collapsed. In the disk that would become our solar system, the center accumulated one to two solar masses after an additional 104 years and became opaque to its own radiation. Consequently, the central temperature rose to about 10,000 kelvins, and the collapsing mass became a protostar within another 105 years.