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Supermoons of 2016

Are supermoons hype? In our opinion … no, just modern folklore. And they cause real physical effects, such as larger-than-usual tides.

July 2016 full moon on the morning of July 19. Photo via EarthSky Facebook friend Kristal Alaimo-Moritz? at Sepulveda Basin Wildlife Reserve, Van Nuys, California.

Full moon, via Kristal Alaimo-Moritz at Sepulveda Basin Wildlife Reserve, Van Nuys, California.

What’s a supermoon? It’s a new or full moon closely coinciding with perigee – the moon’s closest point to Earth in its monthly orbit. An astrologer, Richard Nolle, coined the term supermoon over 30 years ago, but now many in astronomy use it as well. Are supermoons hype? In our opinion … gosh, no, just modern folklore. They’ve entered the popular culture (check out Sophie Hunger’s music video in this post, for example). And they can cause real physical effects, such as larger-than-usual tides. In ancient times, astronomers used an instrument called a diopter to measure the moon’s angular diameter, noting the variation in size of close and far moons. According to the definition of supermoon coined by Nolle, the year 2016 has a total of six supermoons. The new moons of March, April and May and the full moons of October, November and December all qualify as supermoons. Follow the links below to learn about the supermoons of 2016.

What is a supermoon?

What did astronomers call these moons before we called them supermoons?

When are the supermoons of 2016?

Spring tides accompany the supermoons.

Dates of closest full supermoons in past and future years

What is a Black Moon?

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Photographs or other instruments can tell the difference between a supermoon and ordinary full moon.  The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left).  Image by Marco Langbroek of the Netherlands via Wikimedia Commons.

Photographs or other instruments can tell the difference between a supermoon and ordinary full moon. The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Image by Marco Langbroek of the Netherlands via Wikimedia Commons.

What is a supermoon? We confess: before a few years ago, we in astronomy had never heard that term. To the best of our knowledge, astrologer Richard Nolle coined the term supermoon over 30 years ago. The term has only recently come into popular usage. Nolle has defined a supermoon as:

… a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit.

That’s a pretty generous definition, which is why there are so many supermoons. By this definition, according to Nolle:

There are 4-6 supermoons a year on average.

Some astronomers have complained about the name … but we like it! And it’s entered the popular culture. for example, Supermoon is the title track of Sophie Hunger’s new album, released in May, 2015. It’s a nice song! Check it out in the video below.

What did astronomers call these moons before we called them supermoons? We called them a perigee full moon, or a perigee new moon. Perigee just means “near Earth.”

The moon is full, or opposite Earth from the sun, once each month. It’s new, or more or less between the Earth and sun, once each month. And, every month, as the moon orbits Earth, it comes closest to Earth. That point is called perigee. The moon always swings farthest away once each month; that point is called apogee.

No doubt about it. Supermoon is a catchier term than perigee new moon or perigee full moon.

We first became familiar with the supermoon label in the year 2011 when the media used it to describe the full moon of March 19, 2011. On that date, the full moon aligned with proxigee – the closest perigee of the year – to stage the closest, largest full moon of 2011.

About three or four times a year, the new or full moon coincides closely in time with the perigee of the moon—the point when the moon is closest to the Earth. These occurrences are often called 'perigean spring tides.' The difference between ‘perigean spring tide’ and normal tidal ranges for all areas of the coast is small. In most cases, the difference is only a couple of inches above normal spring tides.  Image and caption via NOAA.

About three or four times a year, the new or full moon coincides closely in time with the perigee of the moon—the point when the moon is closest to the Earth. These occurrences are often called ‘perigean spring tides.’ The difference between ‘perigean spring tide’ and normal tidal ranges for all areas of the coast is small. In most cases, the difference is only a couple of inches above normal spring tides. Image and caption via NOAA.

When are the supermoons of 2016? By Nolle’s definition, the new moon or full moon has to come within 361,524 kilometers (224,641 miles) of our planet, as measured from the centers of the moon and Earth, in order to be considered a supermoon.

By that definition, the year 2016 has a total of six supermoons. The first supermoon, for 2016, comes with the March 9 new moon. The new moons on April 7 and May 6 are also considered supermoons, according to Nolle’s definition, and that same definition dictates that the full moons of October, November and December will be supermoons, too. Thus, the full moon supermoons – aka near-perigee full moons – in 2016:

Full moon of October 16 at 4:23 UTC

Full moon of November 14 at 13:52 UTC

Full moon of December 14 at 00:05 UTC

The full moon on November 14, 2016, will present the closest supermoon of the year (356,509 kilometers or 221,524 miles). What’s more, this November 14, 2016 full moon will showcase the moon at its closest point to Earth thus far in the 21st century (2001 to 2100), and the moon won’t come this close again until the full moon of November 25, 2034.

Want more detail? Okay. In 2016, the moon comes closest to Earth on November 14 (356,509 kilometers), and swings farthest away some two weeks before, on October 31 (406,662 kilometers). That’s a difference of 50,153 kilometers (406,662 – 356,509 = 50,153). Ninety percent of this 50,153-figure equals 45,137.7 kilometers (0.9 x 50,153 = 45,137.7). Presumably, any new or full moon coming closer than 361,524.3 kilometers (406,662 – 45,137.7 = 361,524.3) would be “at or near (within 90% of) its closest approach to Earth.”

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

Spring tides will accompany the supermoons. Will the tides be larger than usual at the March, April and May 2016 new moons and the October, November and December 2016 full moons? Yes, all full moons (and new moons) combine with the sun to create larger-than-usual tides, but closer-than-average full moons (or closer-than-average new moons) elevate the tides even more.

Each month, on the day of the new moon, the Earth, moon and sun are aligned, with the moon in between. This line-up creates wide-ranging tides, known as spring tides. High spring tides climb up especially high, and on the same day low tides plunge especially low.

The closest new moon of the year on April 7 and the year’s closest full moon on November 14 are bound to accentuate the spring tide all the more, giving rise to what’s called a perigean spring tide. If you live along an ocean coastline, watch for high tides caused by the November 14 perigean full moon.

Will these high tides cause flooding? Probably not, unless a strong weather system accompanies the perigean spring tide. Still, keep an eye on the weather, because storms do have a large potential to accentuate perigean spring tides.

Dates of closest full supermoons in past and future years. More often than not, the one day of the year that the full moon and perigee align also brings about the year’s closest perigee (also called proxigee). Because the moon has recurring cycles, we can count on the full moon and perigee to come in concert in periods of about one year, one month and 18 days.

Therefore, the full moon and perigee realign in periods of about one year and 48 days. So we can figure the dates of the closest full moons in recent and future years as:

March 19, 2011

May 6, 2012

June 23, 2013

August 10, 2014

September 28, 2015

November 14, 2016

January 2, 2018.

There won’t be a perigee full moon in 2017 because the full moon and perigee won’t realign again (after November 14, 2016) until January 2, 2018.

Looking further into the future, the perigee full moon will come closer than 356,500 kilometers for the first time in the 21st century (2001-2100) on November 25, 2034 (356,446 km). The closest full moon of the 21st century will fall on December 6, 2052 (356,425 km).

By the way, some astronomers will call all the full moons listed above proxigee full moons.

But, like many of you, we’ll have fun just calling ’em supermoons.

What most call a Blue Moon isn't blue in color. It's only Blue in name. This great moon photo from EarthSky Facebook friend Rebecca Lacey in Cambridge, Idaho.

What does a full supermoon look like? Most astronomers say you can’t really detect any difference with your eye between a supermoon and any ordinary full moon, although some careful observers say you can. This great moon photo is from EarthSky Facebook friend Rebecca Lacey in Cambridge, Idaho.

What is a Black Moon? We had never heard the term Black Moon until early 2014. It doesn’t come from astronomy, or skylore, either. Instead, according to David Harper, the term comes from Wiccan culture. It’s the name for the second of two new moons in one calendar month. January 2014, for example, had two new moon supermoons, the second of which was not only a supermoon, but a Black Moon. Does a Black Moon have to be a supermoon in order to be called Black? No. You can read more about Black Moons here.

The next Black moon by the above definition will occur on October 30, 2016. Sten Odenwald at astronomycafe.net lists some other names for the second new moon in a month: Spinner Moon, Finder’s Moon, Secret Moon.

However, we’ve also come across another definition for Black Moon: the third of four new moons in one season. This last happened with the new moon supermoon of February 18, 2015, because this particular new moon was the third of four new moons to take place between the December 2014 solstice and the March 2015 equinox. The next Black Moon by this definition will occur on August 21, 2017, to feature a Black Moon total solar eclipse in the United States.

Bottom line: The term supermoon doesn’t come from astronomy. It comes from astrology, and the definition is pretty generous so that there are about 6 supermoons each year. This post explains what a supermoon is, how many will occur in 2016, which moon is the most “super” of all the 2016 supermoons, and gives a list of upcoming full supermoons for the years ahead.

Learn more: Tides and the pull of the moon and sun

Bruce McClure

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