Answer: Due to a transfer of Earth's rotational momentum to the Moon's orbital momentum as tidal friction slows the Earth's rotation. That increase in the Moon's speed is causing it to slowly recede from Earth (about 4 cm per year), increasing its orbital period and the length of a month as well. In orbital mechanics, a gain in speed results in a higher orbit. The slowing rotation of the Earth results in a longer day as well as a longer month. Once the length of a day equals the length of a month, the tidal friction mechanism will cease. That's been projected to happen once the day and month both equal about 47 days, billions of years in the future. If the Earth and Moon still exist, the Moon's distance will have increased to about 135% of its current value.
