On Wednesday, August 30th, we will have the opportunity to witness a ‘Supermoon.’ It’s a word, or more specifically, a branding, that has emerged relatively recently. Its origin comes not from astronomy, but rather from astrology. It was coined by an astrologer who whimsically defined it as the ‘Full Moon’ that occurs when the moon is in a certain proximity (perigee) to Earth at or near its closest angle of view with the Moon, typically within 90 percent.
In reality, on the fifth Wednesday of August at 12:00 PM ET, the Moon will reach perigee, which is the closest point in its elliptical orbit to Earth, at a distance of about 221,942 miles (357,181 kilometers). And 9 hours and 36 minutes later, the Moon will officially be full. While a full moon astronomically only lasts a moment, that moment is imperceptible to casual observation, and for a day or two before and after, most will refer to the moon as ‘full’: the illuminated strip is so narrow and changing so slowly that it’s hard to tell if it’s present or where it is.
Aside from its ‘Supermoon’ status, this particular full moon will be the second full moon of the month, with the first occurring on August 1st. As a result, the second full moon of August on the 30th will also be branded as the ‘Blue’ Moon. So, fittingly, it will be our ‘Super Blue Moon.’
However, unless there’s an unusual atmospheric condition like dust, smoke, or haze, the moon won’t appear blue but rather a typical pale yellow-white. Nevertheless, due to the media’s hyperbole, many people will be excited to catch a glimpse of this larger moon at the end of summer.
This inundation is for you.
But there’s a catch: when a full moon coincides with perigee, as it does in perigee, this means that around August 30th for several days, tidal ranges will be significantly larger than normal; low tides will be unusually low, while high tides will be unusually high, possibly causing minor coastal flooding.
This kind of extreme tide is referred to as a perigean spring tide, with ‘spring’ derived from the German word ‘springen,’ meaning ‘to jump,’ and it’s not—as is often mistakenly believed—a reference to the season of spring. During these times, spring tides occur when the Moon is full and new, creating a line between the Earth, the Moon, and the Sun, causing their tidal influences to combine. (The Sun exerts only about half the tidal force of the Moon.) On the other hand, a ‘neap tide’ occurs when the Moon is in its first and last quarters and works at cross-purposes with the Sun. During these times, tides are weaker.
The tidal force varies inversely with the cube of the distance to an object. On Wednesday, the Moon’s tidal force at perigee is nearly 14 percent greater than its force at apogee. So, two weeks ago, around August 16th, when the spring tide was close to perigee, it exerts about 48 percent more tidal force during the spring tide of August 30th compared to the spring tide during the Full Moon of August 16th.”
And if there’s an important storm or hurricane looming, which is already interacting with high water levels, it could lead to turbulent seas, shoreline erosion, and significant flooding.
We can only hope that weather conditions this year won’t lead to such situations. However, it’s worth mentioning that the peak of the Atlantic hurricane season typically arrives just a little over two weeks away, around September 10th.
“Supermoon” Branding Takes a “Backseat”
For years, astronomers have labeled the Full Moon that coincides with perigee as the “Perigean Full Moon”. A term that didn’t receive much attention.
Now, it seems that whenever a Full Moon coincides with perigee, it’s being called a “Supermoon.” Some news outlets – in their effort to grab attention – refer to this event as “rare,” though in reality, it happens within a few hours of the Moon reaching perigee, making it not as rare as it might sound.
In fact, this occurs approximately every 413 days.
The next time this happens after Wednesday, will be on October 17, 2024.
Moreover, the Full Moon of August 1, which was about 11 hours ahead of perigee, and also September 29’s Full Moon, which comes roughly 33 hours after perigee, are being labeled as Supermoons as well. This is because they occur within about 90% of the closest distance of the Moon to Earth. In other words, within the top 10% of closest Full Moons in a given year.
So now, in most years, we don’t just have one, but four “Supermoons.” Some years might have as few as two, while others might have as many as five!
But just how “rare” or “super” is that?
Unrealistic Expectations: A Bigger Deal?
And while Wednesday’s Moon – the “biggest Full Moon of 2023” as stated by the Observer’s Handbook of the Royal Astronomical Society of Canada – will be about 14% larger in apparent size than the apogee Full Moon (the Moon’s farthest point from Earth), it won’t be visually distinguishable in terms of its distance from Earth.
So if you step out on Wednesday night, hoping to see the Moon and expecting something extraordinary, you might be disappointed. Before the “Supermoon” terminology, there are often plenty of photos online that show greatly enlarged Full Moons, taken with telephoto lenses, making the Moon appear significantly larger in the sky.
In fact, due to a lack of prior knowledge about the proximity of the Full Moon, most people might not notice a difference between Wednesday’s Full Moon and any other Full Moon. However, once the “Supermoon” idea is suggested, those very people might step outside, look up, and exclaim that the Moon looks much larger than usual; much like the phrase “new clothes of the Emperor” has become a metaphor for logical fallacies.
Bright?
Now, let’s talk about the Moon’s shine. Websites say that a “Supermoon” appears “30% brighter than other Full Moons.” However, this increase in brightness is roughly equivalent to about three-tenths of a percent in actual size; therefore, the Moon’s light on Wednesday night won’t be exceptionally bright.
Still, there might be some who expect to witness an extraordinarily radiant Full Moon that night. In June 2013, a friend told me she was hoping that that year’s “Supermoon” edition would be ‘extremely luminous’, like ‘three-sided light bulbs’; I thought it would be like turning the moon into a staircase of light.
Instead, the Moon’s glow wasn’t noticeably different from previous nights.
The Moon Illusion
Wednesday’s Moon can still appear large, but for a different reason.
When the perigee Moon is near the horizon, it can appear absolutely huge. This well-known “Moon illusion” creates a genuinely striking spectacle when combined with reality. Due to reasons not fully understood by astronomers or psychologists, a slightly larger Moon, hanging lower near trees, buildings, and other foreground objects, can seem incredibly massive.
The fact is, Wednesday’s Moon will be very close to normal, contributing to this curious effect.
So, either a perigee Moon rising at sunset or setting at sunrise can create the illusion that the Moon is so close you could touch it. You can check this for yourself by noting the times of moonrise and moonset for your area on the Don’t Overlook Saturn!
A Full Moon is opposite the Sun in the sky. As it turns out, just three days before reaching this point in its orbit, Saturn will also reach opposition when it’s also opposite the Sun in the sky. So, on Wednesday night, Saturn will “photobomb” the Moon, positioned to its upper right by about five and a half degrees. Undoubtedly, Saturn is much farther from us than our closest neighbor, Earth; it will be at a distance of 814.6 million miles (1.31 billion km) or about 73 light minutes away. This majestic sphere will gleam like a serene yellow-white “star”. Its famous rings will be tilted toward Earth at a 9-degree angle and will be visible through high-power binoculars or even small telescopes with at least 25x magnification.