Despite the moon's relatively weak gravitational force, the moon is close enough to Earth to produce tides in Earth's waters. The average distance from the center of Earth to the center of the moon is 238,897 miles (384,467 kilometers) (at the picture above, you can see distance between earth and moon). That distance is growing but extremely slowly. The moon is moving away from Earth at a speed of about 1 1/2 inches (3.8 centimeters) per year and the moon is about 4.6 billion years old.


 But how we know?
The distance to the moon is measured to an accuracy of 5 centimeters by a laser beam sent from Earth. The beam bounces off a laser reflector placed on the moon by astronauts (Apollo program), and returns to Earth.
  The moon is moving away from Earth

                 click on the picture to enlarge

           click on the picture to enlarge

 The reason?
Gravitational coupling between the Moon and the oceans affects the orbit of the Moon. From the Moon's point of view, the tidal bulges are carried ahead by the rotation of the Earth, so that they don't point directly toward the Moon.
The gravitational coupling drains kinetic energy and angular momentum from the Earth’s rotation. In turn, angular momentum is added to the Moon's orbit. Somewhat counter intuitively, this moves the Moon to a higher orbit with a longer period.
This results in a 3.8 cm yearly increase in the distance between the two bodies.
The Moon will continue to move slowly away from the Earth until the tidal effects between the two are no longer of significance, whereupon the Moon's orbit will stabilize.
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