The tide is the regular rising and falling of the ocean's surface caused by the Moon's gravity (and to a lesser degree the Sun's). The maximum water level is called high tide; the minimum level is low tide. At any given point on the ocean, there are normally two high tides and two low tides each day. On average, high tides occur 12 hours 24 minutes apart. The 12 hours is due to the Earth's rotation, and the 24 minutes to the Moon's orbit. It is often assumed that the tides are simply the Moon's gravitational force pulling the oceans' water toward itself, but this is wrong. Were it so, there would only be one high tide every 24 hours (imagine the water around the Earth with a single bulge pointing towards the Moon). Instead, the tide is caused by tidal forces, which are due to the difference in gravitational attraction on the near and far sides of a body. The tidal force produces two bulges: one pointing towards the Moon, and one pointing away. This is also why the Moon is the major cause of the tides: at the Earth's surface the straightforward gravitational attraction of the Sun is considerably larger than that of the Moon, but the difference in the Moon's grativational force from the near side of the Earth to the far side is much greater than the Sun's