From the Greek word planasthai (πλανᾶσθαι), meaning "to wander," the planets were called "wanderers" by the ancient astronomers because they moved around in the night sky, unlike other "fixed" stars that formed the constellations. Because of this, they were thought to be alive in the heavens, and thus gods, prompting the Romans to give them divine names like Jupiter, Mars, Neptune, Mercury, and Venus.