Because the Moon's mass is a considerable fraction of that of Earth (about 1:81), the two bodies can be regarded as a double planet system, rather than as a planet with a satellite. The plane of the Moon's orbit around Earth lies close to the plane of Earth's orbit around the Sun (the ecliptic), rather than in the plane of the earth's rotation (the equator) as is usually the case with planetary satellites. The mass of the Moon is sufficiently large, and it is sufficiently close, to raise tides in the matter of Earth. Foremost among such matter, the water of the oceans bulges out towards and away from the Moon. The average near-side bulge peak is moments after passing the Moon overhead, and Earth rotates over and under these bulges (in all but the far south and north split up by the north-south land masses) in just over a day. However, this rotation sees set in motion the bulges ahead of the position directly under the Moon as every tidal bulge has an inertia meaning it does not recede instantly. At every point in time this means the far more operative bulge, the moon-facing bulge, is offset from the line through the centers of Earth and the Moon, namely ahead of the Moon's orbit. Because of this, the gravitational pull of this nearer (so gravitationally important) tidal bulge and the Moon is not quite parallel to the Earth–Moon line, i.e. exerting torque between Earth and the Moon. This torque boosts the Moon in its orbit and slows the rotation of Earth.