Earth is intimately tied to the star around which it revolves, the Sun, and the satellite that revolves around Earth itself, the Moon. Without the Sun, of course, life on Earth simply could not exist, not just because of the need for light but to an even greater degree because of the energy it supplies. For that matter, Earth itself would not exist: our planet appears to have developed from the same cosmic cloud that formed the Sun, and without the Sun to hold it in place with its gravitational pull, Earth would go spinning off into space. For all its influence on human life, however, the Sun has less impact on the tides than the Moon, which is smaller but much closer. Together, these two bodies literally define time in human experience, which has been marked by the movements of the Sun and Moon from a time before civilization began.