Today, we know what planets are: other worlds. But, that knowledge is pretty recent in terms of human history. Up until the 1600s, planets seemed like mysterious lights in the sky to early stargazers. They appeared to move through the sky, some more rapidly than others. The ancient Greeks used the term "planetes", which means "wanderer", to describe these mysterious objects and their apparent motions. Many ancient cultures saw them as gods or heroes or goddesses.