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Lunar Perigee and Apogee

The Moon's orbit around Earth is elliptical. The point of the orbit closest to Earth is called perigee, while the point farthest from Earth is known as apogee.

Illustrative comparison of a Supermoon and Micromoon.

A Supermoon versus a Micromoon.

A Full Moon looks bigger and brighter when it occurs around perigee and smaller and dimmer at apogee.

Elliptical Orbit

The Moon's orbit around Earth is elliptical, with one side closer to Earth than the other.

As a result, the distance between the Moon and Earth varies throughout the month and the year. On average the distance is about 382,900 kilometers (238,000 miles).

The point on the Moon's orbit closest to Earth is called the perigee and the point farthest away is the apogee.

Supermoons & Micromoons

The Moon's phase and the date of its approach to its perigee or apogee are not synced. When a Full Moon or New Moon occurs close to the Moon's perigee, it is known as a Supermoon. Oppositely, when a Full Moon or New Moon occurs close to the Moon's apogee, it is known as a Micromoon.

Illustration indicating the difference between a Supermoon and a Micromoon's distance from Earth.
The difference between apogee and perigee.
The difference in Moon's Distance–from its center–to the center of the Earth, at perigee and apogee.
timeanddate.com IMAGE NOT TO SCALE

The Moon passes through its perigee and apogee about once a month. The time it takes for the Moon to complete an orbit, from perigee to perigee, is called the anomalistic month.

Close to Earth

The Supermoon on November 14, 2016, will be the closest a Full Moon has been to Earth since January 26, 1948. The next time a Full Moon is even closer to Earth will be on November 25, 2034 (dates based on UTC time).

Moonrise is the best time to view the Moon, weather permitting, of course. At this time, illusion mixes with reality to make a low-hanging Moon that looks unnaturally large when compared to foreground objects.

Lunar Libration

In addition to its counterclockwise orbit around 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.

When the Moon rocks slightly from north to south and wobbles a little from east to west, it is called lunar libration. This motion makes it possible, over time, to see up to 58% of the Moon’s surface from Earth, but only 50% at a time.

Tidal Effects

The Full Moon lighting up the ocean.
Moon's gravitational pull causes tides.
Moon's gravitational pull causes tides.
©bigstockphoto.com/duallogic

The tides on Earth are mostly generated by the Moon’s gravitational pull. The Moon’s gravity can cause small ebbs and flows in the continents called land tides or solid Earth tides. These are greatest during the Full and New Moons because the Sun and Moon are aligned on the same or opposite sides of Earth.

When the Moon is closer to Earth, the gravitational pull leads to larger variation between high and low tides. It also causes higher spring tides, known as perigean spring tide or the more colloquial term, king tide. It has nothing to do with the season spring, but rather it is a synonym to jump or leap. King tides may cause abnormally high flooding in coastal areas.

On the other hand, when the Moon is at its apogee, the lower gravitational pull leads to lower tides and a smaller variation between high and low tides, known as neaps or neap tide, from Anglo-Saxon, meaning without the power.

Natural Disaster Trigger?

Although the Sun and the Moon’s alignment cause a small increase in tectonic activity, the effects of the Supermoon on Earth are minor. Many scientists have conducted studies and haven’t found anything significant that can link the Super Moon to natural disasters.

According to NASA, the combination of the Moon being at its closest and at Full Moon, should not affect the internal energy balance of the Earth since there are lunar tides every day.

Topics: Astronomy, Moon

Next Perigee

Dec 12, 2016 at 6:28 pm

Distance: 358,461 km / 222,737 mi

Next Apogee

Dec 25, 2016 at 12:54 am

Distance: 405,870 km / 252,196 mi

Apogees and Perigees in 2016

Times for Apogee/Perigee can vary by time zone. Dates are based on the local time in Washington DC. Change location

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The Moon

  1. The Moon Phases
  2. What Is a Supermoon?
  3. What Is a Micro Moon?
  4. Is a Blue Moon blue?
  5. The Moon's Orbit
  6. What Is a Black Moon?
  7. What are Moonbows?
  8. Full Moon Names

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