What are Supermoons and how often do they occur?

What are Supermoons and how often do they occur?

The Moon is the stuff of dreams. We invent stories about it, pretend it is made entirely of cheese, make paper-mâché models of it, and dream of inhabiting it.

The Moon is a big deal—it is an encompassing force that controls the tides, preserves the Earth’s place in the universe as a livable planet, regulates our circadian rhythms, and marks a New Year for many cultures.

January 21st marked Lunar New Year 4721. That night, a new moon supermoon was a mere 221,561 miles from the Earth, the closest a new moon has been to our home since the year 1030, which was 997 years ago for those who don’t want to do the math.

What is a Supermoon?

When astronomer Richard Noelle began using the term supermoon in 1979, he defined it as “both a new and a full moon occurring at or near (within 10% of) perigee.” Perigee is the point in the Moon’s orbit where it is closest to the Earth. When a full moon appears in the sky at or near perigee, it appears up to 14% larger and 30% brighter than a full moon at its furthest distance from the Earth in orbit (known as the apogee). It is important to note that the same is true for the new moon, but its alignment with the Earth and Sun makes it difficult for us to see.

However, the term supermoon is not an official astronomical definition of the lunar event. The scientific name is perigee-syzygy of the Earth-Moon-Sun system, where syzygy means the Earth, Moon, and Sun are perfectly aligned in the sky—at perigee.

It is also important to note that the opposite effect also occurs. When the full moon is the furthest from the Earth (apogee), it appears smaller than the “average” moon, and this lunar event is called a micromoon.

How Often do Supermoons Occur?

While it is easy to picture the orbit of a planet or moon as a circle, orbits are elliptical and vary over time. Therefore, not every full moon coincides with perigee—or even within 10% of perigee. Supermoons do not occur in a monthly cyclical pattern, but they do follow an approximate yearly pattern. Supermoons occur during consecutive months each year, and, depending on the timing of the orbit, 3 or 4 supermoon events will take place.

Under the strictest astronomical definition of perigee-syzygy, the Sun, Moon, and Earth perfectly align approximately once every 14 months. Using the broader criteria of Noelle’s supermoon, and according to The Farmer’s Almanac, four full moon supermoons will be visible in 2023.

2023 Full Moon Supermoon Dates:

  • July 3rd
  • August 1st
  • August 31st (A blue moon and the closest and brightest full moon in 2023)
  • September 29th

Are Supermoons Supersized?

No. A supermoon appears larger due to the simple fact that it is closer to us in the sky than during a regular full moon.

The same can be said for any object in your home or with the MOVA Moon Globe (pictured above).

MOVA Moon Globe Size Experiment:

  1. Sit at a table or desk. Place your MOVA Moon Globe about 12 inches away from you. Look at the Moon Globe.
  2. Pick up your MOVA Moon globe and place it within an inch of your face. It appears larger than it did sitting in the base.
  3. Move the MOVA Moon Globe to the far side of the room and return to your original seat. Look at the Moon Globe, it appears to be the smallest of all three.

A supermoon is, in fact, the same Moon with the same size—measuring in with a diameter of 2,159 miles and roughly ¼ the size of the Earth. Just like your MOVA Moon Globe is the same size during the experiment.

Astronomers measured the perceived difference of a supermoon to be around 7% larger than a regular full moon and 14% larger than a micromoon.

As a side note, many of us also experience Moon Illusion. Moon Illusion is a phenomenon where the perceived size of a full moon grows at or near the horizon (as the Moon is rising or setting). The Moon appears larger because our brains naturally enlarge objects near a skyline—be it buildings or trees.

Are Supermoons Superbright?

Yes, unlike the illusion that a supermoon is larger, a supermoon does cast more light on Earth. In fact, a supermoon is 30% brighter than a micromoon. And it is easily explained by science. 

As the Moon moves closer to the Earth, more of the light reflected off the Moon reaches the Earth.  One of the brightest (and closest) full moon supermoon events took place on November 14, 2016, when the moon was only 221,525 miles away.

Do Supermoons Have Superstrength?

When the Moon is in perigee, it has a greater gravitational pull on the Earth. Both new moon and full moon supermoons cause variations in tides by up to two inches. While the increase in high tides is most easily seen, the change also affects low tide levels.

The higher tides affiliated with supermoons are often called king tides. King tides cause an unusually high level of water along coastal areas, resulting in tidal flooding. As the climate changes and sea levels rise, the effects of king tides become more severe.

Back in 1979, when Noelle named the supermoon, he also theorized that the extra gravitational pull could cause earthquakes. In 2011, he stated that the supermoon on March 19th played a role in the earthquake and tsunami that struck Japan 8 days earlier. Scientists never found evidence to prove a correlation of those or any other supermoon and earthquake events. In response to Noelle in 2011, Dr. James Garvin, Chief Scientist at NASA Goddard Space Flight Center, replied, The effects on Earth from a supermoon are minor, and according to the most detailed studies by terrestrial seismologists and volcanologists, the combination of the Moon being at its closest to Earth in its orbit, and being in its ‘full moon’ configuration (relative to the Earth and Sun), should not affect the internal energy balance of the Earth, since there are lunar tides every day.’”

What’s in a Name?

Full Blue Supermoon (August 31, 2023): A blue moon is the second full moon in one calendar month. While rare, they are not an unexpected occurrence due to the 29 days the Moon needs to complete one cycle of phases.

Full Strawberry Supermoon (June 14, 2022): Algonquin tribes called the full moon each June a strawberry moon, not because of its color—although moons can appear pink or red when nearing the horizon—but because June was strawberry picking season in their region of America.

Full Flower Supermoon (May 16, 2022): The full moon each May is named the flower moon to signify the flowers that bloom during the month of May.

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