Scientists can accurately calculate the distance between the Earth and the moon by using a specialized reflector array left on the moon's surface during the 1969 Apollo 11 mission. A laser beam aimed at the moon from an optical telescope strikes the reflector and bounces back to Earth. By measuring the round-trip travel time of the laser beam, researchers can determine the distance between the Earth and moon to an accuracy of a little over an inch.
The moon orbits the Earth once every 29.5 days. This period is the lunar month, and each lunar month has an perigee and an apogee. A full moon at perigee appears noticeably larger and brighter than a full moon at apogee. The moon at perigee ranges from 221,500 to 229,000 miles from Earth.
During apogee, the moon is between 245,000 and 253,000 miles from Earth. Due to the gravitational pull of the sun, extreme values for the perigee and apogee occur during the full and new phases of the lunar cycle, and more moderate values occur during the moon's quarter phase. You can use a lunar perigee and apogee calculator to determine when, and during which lunar phase, the moon will be at perigee and apogee.
The swell of the ocean's tides follows the gravitational pull of the moon. At perigee, when the moon is at its closest, tides are higher, and there is greater variation between high and low tides. The moon at apogee exerts less of a pull, and there are lower tides with less variation. Full and new moons enhance the effects of perigee and apogee on tides, and these effects are mitigated when the moon is at quarter phase.