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What Is a Micromoon?

A Micromoon is when a Full Moon or a New Moon coincides with apogee, the point in the Moon's orbit farthest away from Earth.

Full Moon and branches against a dark sky.

Micro Moon: A Full or New Moon at apogee.

©iStockphoto.com/Wouter van Caspel

October 2020 has two Full Moons. Both are Micro Moons—one on October 1 and another on October 31, depending on your time zone. The second Micro Full Moon is also a Blue Moon.

The Farthest Point

The Moon orbits Earth in an elliptical path, which means one side of the path is closer to the Earth than the other.

The point in the Moon's orbit closest to Earth is called perigee, while the point in the orbit farthest from Earth is known as apogee. The average distance between Earth and the Moon is 382,500 kilometers or 237,700 miles.

When a Full Moon or a New Moon occurs around apogee, it's called a Micromoon, Minimoon or Apogee Moon. A Micro New Moon is a good time to stargaze.

A Full or New Moon occurs around perigee is called a Supermoon.

May Look Smaller

Because a Micromoon is further away, it looks approximately 14% smaller than a Supermoon. In addition, the illuminated area appears 30% smaller, so it might look a little less bright.

No Universal Rules

There are no universal rules as to how far away the Moon must be to qualify as a Micromoon. The following definitions are used at timeanddate.com:

  • Micromoon: A Full Moon or New Moon that takes place when the center of the Moon is farther than 405,000 kilometers (ca. 251,655 miles) from the center of Earth.
  • Supermoon: A Full or New Moon that occurs when the center of the Moon is less than 360,000 kilometers (ca. 223,694 miles) from the center of Earth.

Micromoon Affects the Tides

The greatest difference between high and low tide is around Full Moon and New Moon. During these Moon phases, the gravitational forces of the Moon and the Sun combine to pull the ocean’s water in the same direction. These tides are known as spring tides or king tides.

Micromoons lead to around 5 cm (2 inches) smaller variation than regular spring tides, called apogean spring tides.

The tidal range is smallest during the 2 Quarter Moons, known as neaps or neap tide.

Natural Disaster Trigger?

Old folklore accounts suggest that Full Moons and Micromoons affect human mental health and bring on natural disasters, like earthquakes, but no scientific evidence supports any such correlation.

Topics: Astronomy, Moon