In the beginning there is only hydrogen, the most abundant element in the universe. Hydrogen clouds condense, and their increased gravity can attract more hydrogen, starting a chain reaction that forms a star. Hydrogen is still at the center of them, but now the massive pressures and temperatures fuse hydrogen atoms together to make helium, in the process giving out light and heat. Eventually the stars run out of hydrogen to burn, and, if their mass is large enough, collapse on themselves until the pressure becomes so great that the star explodes into a supernova. The result of one such explosion was witnessed by astronomer Johannes Kepler.

On this day, October 17, in 1604 Kepler recorded what he thought was a new star, which was named after him. Kepler’s wasn’t the first observation of the star, but was the most extensive.

For a brief period, the Kepler’s star was one of the brightest objects in the night sky, and could be seen during the daytime. More interestingly perhaps, the explosion witnessed by Kepler took place long before — somewhere between 20,000 and 40,000 years before the light reached Earth. Kepler’s star exploded when homo sapiens were still using stone tools.