All early cultures were exposed to the night sky. The seven celestial objects that are visible to the naked eye and moved in a way that clearly indicated they were not stars were hence known as "planets," or "wandering stars," in the ancient world, and they worked their way into the myths and legends of most early cultures. Time was and still is easily measured by celestial events; the spring equinox for example, occurs approximately every 365 days. It was easy to adapt the other 7 objects clearly seen floating about in the sky to measure the passage of time. The Sun, Moon and five visible planets gave their names to the weekly cycle of days.