Lunar Perigee and Apogee
The Moon's path around the Earth is elliptical, with one side of the orbit closer to Earth than the other. The side closest to the Earth is called the perigee and the side farthest from the Earth is known as the apogee.
On average, the Moon is about 238,800 miles (384,500 km) from the Earth. However, because of the elliptical shape of the Moon's orbit, the actual distance varies throughout the year, between 225,804 miles (363,396 km) at the perigee and 251,968 miles (405,504 km) at the apogee.
A variety of factors affect the Moon's distance from Earth. The Sun's gravitational force over the Moon, the inclination of the Moon's orbit with respect to the Earth's orbital plane, and the gravitational forces of other celestial objects all affect the shape and size of the Moon's orbit, and the distance of the Moon from the Earth.
Lunar Perigee and Apogee
The Moon passes through its perigee and apogee about once a month. The time it takes for the Moon to complete an orbit, perigee to perigee, is called the anomalistic month.
The Moon's phase and the date of its approach to its perigee or apogee are not synced, though sometimes it is possible for a full Moon to occur close to the Moon's perigee. This is known as the Supermoon.
When this happens, the Moon may look larger than a normal full Moon or a micro Moon, a full Moon that occurs at the apogee. From Earth, a supermoon can look up to 12-14% larger and about 25-30% brighter than a micro moon.
In addition to its orbit around the Earth, the Moon rotates around its axis at a constant speed. Like all celestial objects with elliptical orbits, the Moon's speed varies on its path around the Earth - it speeds up when it is at its perigee, and slows down when it is at the apogee. This means that at its perigee, the Moon's orbital speed is faster than its rotational speed.
This causes lunar libration, a slow rocking back and forth of the Moon. This allows an observer on Earth to see slightly different portions of the Moon’s surface at different times. About 58% of the Moon's surface is visible from Earth, though at any given time, you can only see 50% of the Moon.
Libration of Latitude
Libration of latitude does not occur due to the lunar apogee and perigee. Instead, it happens because the Moon's orbit is inclined or slanted by about 5° with respect to the Earth's oribal plane. Libration of latitude allow us to see about 6.5° latitude beyond the Moon's North and South Pole.
Lunar Perigee and Apogee's Effects on Earth
In addition to affecting the apparent size and brightness of the Moon, the lunar perigee and apogee affect the tides. When the Moon is away from the Earth, it has less gravitational pull over Earth. This can lead to lower tides and smaller variations between low and high tide levels. On the other hand, a perigee Moon can cause higher tides and higher low-high tide level variations.
Many people believe that the Moon's position on its orbit can cause extreme weather. There is, however, no scientific proof to back up this claim.
Viewing the Moon's Perigee and Apogee
How to make the best of your time outdoors looking the Moon:
- Use our Moon Distance Calculator and our Moon Phase Calculator to find out the next perigee and apogee Moon, including for full Moons.
- The best time to see the Moon is when it is near the horizon due to atmospheric distortion. At this time, illusion mixes with reality to make a low-hanging Moon that looks unnaturally large when compared to foreground objects. Find Moonrise and Moonset times from anywhere.
- Always check the weather before you step outside to view the Moon.