Astronomy Essentials

What is a supermoon? And when, in 2022?

Bright full moon with a woman and a girl watching it.
View at EarthSky Community Photos. | Radu Anghel in Parjol, România caught what he called “a family photo with the supermoon of July 13, 2022.” Thank you, Radu! Supermoons don’t appear bigger to the eye than other full moons. But they do appear brighter!

New moon happens when the moon (in its monthly orbit of Earth) goes more or less between the sun and Earth.

Full moon happens when the moon (in its monthly orbit) is on the opposite side of Earth from the sun.

Perigee – from the root words peri meaning near and geo meaning Earth – is the moon’s closest point to Earth in a month.

The new or full moon closely coincides with perigee several times each year. When that happens, in the language of popular culture, we have a supermoon.

As it’s used today, the word supermoon was coined by astrologer Richard Nolle in 1979. According to Nolle’s definition, a full moon or new moon is a supermoon when it’s also within 90% of its closest point to Earth. Nowadays, different websites calculate supermoons differently. EarthSky uses supermoon dates as determined by astronomer Fred Espenak. He’s best known for his time at the Goddard Space Flight Center, where he became a world expert on eclipse predictions. His method of calculating supermoons takes into account changes in the moon’s orbit during each lunar cycle.

Love the moon? See its phase for every day in 2022. EarthSky lunar calendars now available! Going fast!

Full supermoons in 2022

Fred Espenak’s full supermoon table gives us these values – dates and moon distances – for full supermoons in 2022. Contrast these moon distances to the average moon distance of 238,900 miles (384,472 km).

May 16 225,015 miles (362,127 km)

June 14 222,238 miles (357,658 km)

July 13 222,089 miles (357,418 km)

August 12 224,569 miles (361,409 km)

The supermoon of May 16, 2022, will undergo a total lunar eclipse, visible from North America.

The supermoon of July 13 will be the closest supermoon for 2022. On that date, full moon and lunar perigee fall on the same day.

New supermoons in 2022

Fred Espenak’s new supermoon table gives us these values – dates and moon distances – for new supermoons in 2022. Contrast these moon distances to the average moon distance of 238,900 miles (384,472 km).

January 2 222,478 miles (358,044 km)

February 1 226,493 miles (364,505 km)

November 23 227,522 miles (366,161 km)

December 23 223,702 miles (360,013 km)

Supermoon: a large full moon, slightly smaller full moon, split moon with one side large and the other small.
Here’s a comparison between the December 3, 2017, full moon at perigee or supermoon (closest to Earth for the month) and the year’s farthest full moon in June 2017 at apogee (farthest from Earth for the month) by Muzamir Mazlan at Telok Kemang Observatory, Port Dickson, Malaysia. More photos of the December 2017 supermoon.

Supermoon hype?

Some astronomers complain about the name supermoon. They like to call supermoons hype. But supermoons aren’t hype. They’re special. Many people now know and use the word supermoon. We notice even some diehards are starting to use it now. Such is the power of folklore.

The hype aspect of supermoons probably stemmed from an erroneous impression people had when the word supermoon came into popular usage … maybe a few decades ago? Some people mistakenly believed a full supermoon would look much, much bigger to the eye. It doesn’t. Nowadays, most people seem to realize that supermoons don’t look bigger to the eye than ordinary full moons.

It’s true experienced observers do say they can detect a difference. But you’d have to be a very keen observer to notice it. Most of us can’t tell any difference inthe size of a supermoon and an ordinary full moon

But … do supermoons do look brighter than ordinary full moons? Yes! By a noticeable amount. A supermoon exceeds the disk size and brightness of an average-sized full moon by some 15%. It exceeds the disk size and brightness of a micro-moon (year’s smallest full moon) by some 30%. So go outside on the night of a full supermoon. Even if you’re a casual observer of the moon, there’s the potential for you to notice the supermoon is exceptionally bright!

For a visual reference, the size difference between a supermoon and micro-moon is proportionally similar to that of a U.S. quarter versus a U.S. nickel. Again, that difference isn’t noticeable to the eye at the moon’s distance. But the brightness difference is noticeable.

By the way, before we called them supermoons, we in astronomy called these moons perigean full moons, or perigean new moons. No doubt about it. Supermoon is catchier.

A boy in a jacket, outside, holding his hands up so that it looks like he's holding the full moon.
Supermoon and friend Sunday evening, by Roxana Soetebeer in Woodstock, New Brunswick, Canada.

High tides from new and full supermoons

What’s more, all supermoons have the potential to cause higher-than-usual tides. High tides during the full or new moon are called spring tides. High tides during a full or new moon at perigee are called perigean spring tides, or, sometimes, king tides. And nowadays you sometimes hear them called supermoon tides.

These perigean or king or supermoon spring tides tend to follow the date of new or full moon by a day or so. These especially high tides are highly dependent on the shapes of local coastlines and on local weather conditions. They tend to follow the supermoons by a day or so.

Do extra-high supermoon tides cause flooding? Maybe yes and maybe no. Flooding typically occurs when a strong weather system accompanies an especially high spring tide.

Diagram showing sun and moon lined up with ocean stretched toward moon.
Around each new moon (left) and full moon (right) – when the sun, Earth, and moon are located more or less on a line in space – the range between high and low tides is greatest. These are called spring tides. A supermoon – new or full moon at its closest to Earth – accentuates these tides. Image via physicalgeography.net.
Two diagrams: Perigee on sun side of earth (new) and perigee opposite the sun (full).
About 3 or 4 times a year, or more often, a new or full moon coincides with the moon’s closest point to Earth, or perigee. There’s usually only a small difference – typically a couple of inches (or centimeters) – between these “perigean spring tides” and normal tidal ranges. But, at these times, if a storm strikes along a coastline, flooding can occur. Image via NOAA.

How often do we have supermoons?

Often! But it also depends on your definition of supermoon.

Here’s a list of each year’s closest full supermoon perigees from 2010 to 2022 (from Espenak’s full supermoon table):

January 30, 2010 (356,607 km or 221,585 miles)

March 19, 2011 (356,580 km or 221,569 miles)

May 6, 2012 (356,954 km or 221,801 miles)

June 23, 2013 (356,991 km or 221,824 miles)

August 10, 2014 (356,898 km or 221,766 miles)

September 28, 2015 (356,878 km or 221,754 miles)

November 14, 2016 (356,523 km or 221,533 miles)

December 3, 2017 (357,987 km or 222,443 miles)

January 2, 2018 (356,604 km or 221,583 miles)

February 19, 2019 (356,846 km or 221,734 miles)

April 8, 2020 (357,035 km or 221,851 miles)

May 26, 2021 (357,462 km or 222,117 miles)

July 13, 2022 (357,418 km or 222,089 miles)

People standing on a modernistic building and oceanfront sidewalk watching moonrise under a distant bridge.
Henrique Silva wrote from Portugal in 2016: “The first supermoon rising drives everybody’s attention from the brand new Lisbon’s MAAT – Museum of Art, Architecture and Technology – designed by the architect Amanda Levete from London. Over the past week there was great excitement with the new building, but tonight the moon was the real star! In October 2016, the moon’s perigee came about 19 hours after full moon. The close coincidence of full moon and perigee makes this October full moon a supermoon!”

The recurring cycle of supermoons

The full moon supermoon series of 2022 will recur after 14 lunar months (14 returns to full moon). That’s because 14 returns to full moon almost exactly equal 15 returns to perigee, a period of about one year, one month, and 18 days.

The mean lunar month (full moon to full moon, or new moon to new moon) = 29.53059 days, whereas the mean anomalistic month (perigee to perigee, or apogee to apogee) = 27.55455 days. Hence:

14 lunar months (14 returns to full moon) x 29.53059 days = 413.428 days
15 anomalistic months (15 returns to lunar perigee) x 27.55455 days = 413.318 days

Given that supermoons recur in cycles of 413 days (about one year, one month and 18 days), we can can expect the full moon supermoons to come about one month and 18 days later next year, in 2023.

Two children in a field reaching up to a full moon.
A supermoon is a new or full moon at its closest to Earth for the month. Does it look bigger than usual? No. But are supermoons brighter than ordinary full moons? Yes! Photo by Rebecca Lacey in Cambridge, Idaho. Thanks, Rebecca!

Bottom line: For 2022, the full moons of May, June, July and August are supermoons. New moon supermoons of 2022 will be the new moons of January, February, and December. The supermoon of July 13, 2022, is the closest and brightest full supermoon of the year.

Posted 
January 2, 2022
 in 
Astronomy Essentials

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