Definition of galaxy

The word "galaxy" originates from the Greek word "galaxias," meaning "milky." This term was first used by the ancient Greek philosopher Democritus around 450 BCE to describe the Milky Way, a bright, hazy band of light that appears in the night sky. The Greeks believed that the Milky Way was a physical path created by the gods, and the term "galaxy" referred to this luminous ribbon. Later, in the 16th century, the term "galaxy" was used to describe other celestial bodies, such as nebulae and star clusters, which were thought to be smaller versions of the Milky Way. Today, the term "galaxy" refers to any massive, gravitationally bound system consisting of stars, stellar remnants, interstellar gas, dust, and dark matter, typically dominated by a central supermassive black hole.