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Why is the Supermoon so compelling to us?

Tuesday, May 19th 2020, 1:30 pm - Supermoons are one of the most popular events in astronomy and stargazing.

What is a 'supermoon' and why is it so compelling to us?

We just saw the Super Flower Moon, the fourth and final Super Full Moon of 2020. Coming up later this year, there will be three "invisible" supermoons - the three closest New Moons of the year.

If it seems like you've been hearing about Supermoons a lot these days, it's not just a figment of your imagination. In fact, in any given year, there are at least six, and as many as eight, 'super' Moons.

'SUPER SIZED'

A 'Supermoon' is defined as a Full Moon or New Moon that is near or at its closest distance to Earth in its orbit.

It isn't really a term used by astronomers. Instead, it was thought up by astrologer Richard Nolle, in 1979.

Nolle defined a 'super' Moon 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 (perigee)."

SuperFlowerMoon-May72020-NASAGoddardThe May 7-8 Supermoon. Credit: NASA's Scientific Visualization Studio

With the Moon closer than normal at this time, it translates into a Super Full Moon appearing slightly larger in the night sky. Without having a specific reference, however, it's not easy to notice a difference in the Moon's apparent size.

What is more noticeable is the brightness of a Super Full Moon. A Supermoon can appear up to one third brighter than a normal Full Moon!

WATCH BELOW: SEE EVERY VIEW OF THE MOON FOR 2020 IN LESS THAN 5 MINUTES

ASTRONOMICALLY SPEAKING

To put all of this into astronomical terms, a Supermoon is when the Moon reaches its Full or New phase when its distance from Earth is 361,524 km or closer.

This brings up a few questions. Does the Moon's distance to Earth change? If so, why does it change, and by how much?

If you were able to sit in a spaceship and watch Earth and the Moon from high above, it would appear as though the Moon was tracing out a circle in space as it travelled around the planet. As it turns out, though, if you carefully plot where the Moon is at each point in its orbit, it would be revealed that it actually travels along an ellipse.

The Moon's average distance from Earth is considered to be 384,400 km. During each of these elliptical orbits, however, the Moon spends roughly half of the time a little closer than that, and the rest of the time a little bit farther away.

The astronomical term for when the Moon is at its closest distance to Earth during any particular orbit is perigee. The opposite point, when it is farthest from Earth on a particular orbit, is called apogee.

Moon-Orbit-2020This diagram of the Moon's slightly elliptical orbit around Earth shows the closest perigee and farthest apogee distances for 2020. Credit: NASA's Scientific Visualization Studio/Scott Sutherland

From here on the surface of Earth, we can't watch the Moon travel in the same way, but it's still possible to keep track of this elliptical orbit. We do this by watching the apparent size and brightness of the Moon in the night sky. When the Moon is closer, it will appear larger and brighter, and when it is farther away it will appear smaller and dimmer.

Since the Moon is not only influenced by Earth's gravity, but also the gravitational pull of the Sun, and the other planets in the solar system, each orbit around Earth is ever so slightly different from the last. As a result, the Moon's orbital ellipse changes, month by month. Thus, the timing and distance of the Moon's perigee and apogee also change, month by month.

The Moon's perigee distances from Earth tend to be between 356,400–370,400 km, but they can be even closer at times. The closest lunar perigee on record, so far, was 356,378 km, on January 4, 1912. The next time a perigee Full Moon gets closer will be January 1, 2257, when it reaches a distance of 356,372 km.

Apogee, on the other hand, varies between about 404,000–406,700 km. Even these are just averages, though. The absolute farthest apogee on record will be on February 3, 2125, at a distance of 406,718 km.

2020-Perigee-Apogee-FullMoon-CompareThis visualization directly compares the sizes of the April 7-8 Perigee Full Moon and October 30-31 Apogee Full Moon. Credit: NASA's Scientific Visualization Studio/Scott Sutherland

In 2020, there are four Super Full Moons, with the closest perigee Full Moon on the night of April 7-8, when it reaches a distance of 357,042 km.

For comparison, the farthest apogee Full Moon is on October 31 - Halloween - at a distance of 406,163 km. (If you're keeping track, although the February Full Moon occurs in the early morning of the 9th, a full day and a half before the perigee Moon, the Moon is still 99.6% full when it rises on that night.

2020-Supermoons-MinimoonsCredit: NASA's Scientific Visualization Studio/Scott Sutherland

Not that anyone will see them, since they will be lost in the daytime glare of the Sun, but there are also three Super New Moons in 2020, as well - on September 16, October 16 and November 15.

WHY THE FASCINATION?

Since there are three of them, at least, every year, Supermoons certainly cannot be considered a rare occurrence. Even when they do occur, it is often difficult to actually tell that the Moon actually looks bigger, since we don't have an easy way to make a direct comparison (we do tend to notice that it is brighter, though).

There can definitely be more spectacular things to see in the night sky. Meteor showers, lunar eclipses and planetary alignments are just a few that happen on a fairly regular basis. Seeing the full splendour of a glittering sky of stars, with the Milky Way stretching from horizon to horizon, is absolutely awe-inspiring, as well.

So, why are Supermoons so compelling to us?

moonlight-1226253 1920The Full Moon captured on the night of October 13-14, 2019, by Alex Verville.

Besides the Sun, the Moon is our most common and recognizable sight in the sky, day or night. The thinnest Crescent Moon is an amazing sight to behold, and a Full Moon is a wonder to see. Even when we are standing under the brightest lights of the downtown core of a city, where the urban light pollution washes out nearly everything else in the night sky, if the Moon is up, it will still be clearly visible.

For this reason, the Moon is a very important part of our lives. This is especially true for those who usually miss out on all the other astronomical events in a year. Quite simply, it is our most common point of connection with the universe beyond our planet.

So, when something about the Moon changes - even when it is just slightly bigger and brighter in the sky - it attracts our attention as something significant.

WHAT'S IN A NAME?

So, each Full Moon of the year has a name, because of course it does. The May Full Moon is known as the Full Flower Moon.

2020-Full-Moon-Names-1600x900The various Farmer's Almanac Full Moon Names for 2020. Credit: NASA's Scientific Visualization Studio/Scott Sutherland

Now, the claim that these names are based on First Nations lore is a stretch of the truth.

Various indigenous peoples did give names to some or all of the Full Moons of the year. These names were often far more nuanced than a single word descriptor, though. Also, there is no single list from any one nation or language that matches the names presented in the Farmer's Almanac (Old or otherwise).

One important note: These names have been given certain meanings, of course, however whenever the name involves some colour, such as the Full Pink Moon, this has nothing to do with the actual colour of the Moon itself. According to the Farmer's Almanac, April's 'Pink Moon' apparently takes its name from the pink flowers that bloom at this time of year from a plant known as pink moss phlox.

Specific circumstances or conditions in the atmosphere can make the moon appear different colours - orange, pink, blue. Unless the Moon passes through Earth's shadow during a lunar eclipse, it will always be the same shades of grey.

Sources: NASA | Fourmilab

Note: Teaser image for this article is of the March 'Full Worm Moon' courtesy Lynn Beaupre, from Bonnyville, AB, who uploaded the picture into our UGC Gallery. The Moon appears 'pinkish' due to the light being refracted though Earth's atmosphere, as the Moon hangs just above the horizon.

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