1. Eighteenth-century philosopher Immanuel Kant was one of the first people to theorize that the Milky Way was not the only galaxy in the universe. Kant coined the term island universe to describe a galaxy.
2. Astronomers now estimate that there are 100 billion galaxies in the observable universe.
3. One of the earliest uses of the English term Milky Way was in Geoffrey Chaucer’s 14th-century poem “The House of Fame.” He likened the galaxy to a celestial roadway.
