On Wednesday, August 30, you will no doubt hear the mainstream media proclaiming that that night we will have the opportunity to witness a “supermoon”. It is a term, or more precisely a branding, of relatively recent origin. It does not come from astronomy, but from astrology; first coined by an astrologer, who arbitrarily defined it as “a full moon that occurs with the moon at or near (90% of) its closest approach to Earth in a given orbit ( perigee).
Indeed, at noon ET on this fifth Wednesday of August, the Moon will arrive at perigee, its closest point in its orbit to Earth, at 221,942 miles (357,181 km). And 9 hours and 36 minutes later, the moon will be officially full. Although a full moon theoretically lasts only an instant, that instant is imperceptible to ordinary observation, and for about a day before and after most will refer to seeing the nearly full moon as “full”: the shaded band is so narrow, and its apparent width changes so slowly that it is difficult with the naked eye to tell whether it is present or which side it is on.
And in addition to its “supermoon” status, this particular full moon will be the second to occur in August, with the first occurring on August 1. As a result, the second full moon on August 30 will occur on August 30. also be labeled as a “blue” moon. So, for what it’s worth, what we’ll get will be a “Super Blue Moon.”
However, unless there are unusual atmospheric conditions such as airborne dust, ash, or smoke, the moon will not appear blue but in its normal yellow-white form. . Still, thanks to mainstream media hyperbole, many will likely be looking forward to that big late summer moon.
Related: Full moon calendar 2023: When to see the next full moon
If you’re hoping to spot the full moon, our guide to the best binoculars might help you find some great wide-angle optics for viewing larger areas of the lunar surface. Or, if you want to take a closer look at the Moon’s features, our guide to the best telescopes can help you find the equipment you need.
And if you want to take pictures of our natural satellite or the night sky in general, check out our guide on how to photograph the moon, as well as our best cameras for astrophotography and our best lenses for astrophotography.
This flood is for you
But there is also a downside: a full moon almost coinciding with perigee means that for several days around August 30, the tidal range will be much greater than normal; low tides will be unusually low while high tides will be unusually high, possibly resulting in even minor coastal flooding.
Such an extreme tide is known as the perigee living tide, the source word being derived from the German spring – “emerge” and is not – as is often mistaken – a reference to spring. Each month, high tides occur when the moon is full and new. At these times, the Moon and the Sun form a line with the Earth, so their tidal effects add up. (The sun exerts a little less than half the tidal force of the moon.) “Dead tides,” on the other hand, occur when the moon is in first and last quarter and working countercurrent with the sun. . At these times, the tides are low.
The tidal force varies as the inverse of the cube of the distance from an object. On Wednesday, the Moon is 14% closer at perigee than at apogee. As a result, it exerts 48 percent more tidal force during the high tides on August 30 than the high tides near their peak two weeks earlier, on August 16.
And if a major storm or hurricane occurs offshore, acting in concert with already high water levels, the consequences could lead to rough seas, beach erosion and major flooding.
One can only hope that such weather conditions will not materialize this year, although it should be noted that the traditional peak of the Atlantic hurricane season comes less than two weeks later, on September 10.
The “watered down” Supermoon brand
For years, astronomers have classified a full moon coinciding with perigee as a “perigee full moon.” A term that has received little to no fanfare.
Now, it seems that whenever a full moon coincides with perigee, it’s called a “supermoon.” Some presenters – in an apparent effort to grab your attention – call this event “rare,” even though, in reality, the full moon a few hours after arriving at perigee isn’t really such a rare event.
In fact, it happens on average at an interval of once every 413 days or so.
After next Wednesday, the next time this will happen will be October 17, 2024.
And yet, the August 1 full moon, which occurred about 11.5 hours before perigee, as well as next month’s full moon, September 29, which occurs nearly 33 hours after perigee, also qualify. supermoons, apparently because they are 90% of the Moon’s closest approach to Earth. Or in other words, among the 10% closest full moons for a given year.
So most years we have not just one but four “super moons”. Some years there may be only two, while other years there may be as many as five!
But how “rare” or “super” is that?
Unrealistic expectations: higher?
And while Wednesday’s moon will be — as the Royal Astronomical Society of Canada’s Observer’s Handbook suggests — the “largest full moon of 2023” (14% larger in apparent size than a full moon at its apogee – furthest from Earth), the variation in the Moon’s distance is not readily apparent to observers looking directly at the Moon.
So if you go out and watch the moon on Wednesday night and expect to see something special, you’ll probably be disappointed. There are always plenty of images posted on the internet ahead of a “Super Moon,” showing extremely large full moons, all taken with telephoto lenses, all implying that the moon is going to look incredibly large in the sky.
In fact, without prior knowledge of how close the full moon is, chances are most people won’t notice any difference between Wednesday’s full moon and any other full moon. However, once the concept of a “supermoon” is suggested, these same people will come out, look up and declare that the moon do look much taller than normal; in the same way that the expression “the emperor’s new clothes” has become an idiom about logical errors.
Then there is the question of the brightness of the moon. Websites speak of the “supermoon” appearing “30% brighter than other full moons.” But it actually corresponds to a minimal increase less than three tenths of a magnitude; thus, the moonlight on Wednesday evening will not be exceptionally bright.
Still, there are probably those who think they will see an unusually dazzling full moon that night. In June 2013, a friend of mine told me that she expected that year’s version of the “supermoon” to be “radically brighter,” “like with those 3-way bulbs; I thought it would be like turning on the moonlight”. one notch.”
Instead, the moon’s brightness seemed no different than on previous nights.
The moon illusion
Wednesday’s moon might still look huge, but for a different reason.
When the moon at perigee is near the horizon, it can look absolutely huge. It was then that the famous “moon illusion” combines with reality to produce a truly breathtaking sight. For reasons that astronomers or psychologists don’t fully understand, a low moon looks incredibly large when it hovers near trees, buildings, and other foreground objects.
The fact that the Moon is much closer than usual on Wednesday will only serve to amplify this strange effect.
So a moon at perigee, either rising in the east at sunset or sinking in the west at sunrise, can appear to make the moon appear so close that it almost seems like you can touch it. You can check this for yourself by first noting down the moonrise and moonset times for your area by going to this page. US Naval Observatory website.
Don’t neglect Saturn!
A full moon is positioned opposite the sun in the sky. It turns out that three days before the Moon reaches this point in the sky, the planet Saturn will arrive in opposition to the sun, while it is also opposite the sun in the sky. Thus, on Wednesday evening, Saturn will “photobomb” the Moon, located about 5 and a half degrees in the upper right.
Saturn is of course much further away than our nearest neighbour; it will be located 814.6 million miles (1.31 billion km) or 73 light minutes from Earth. The ringed wonder will glow like a calm yellow-white “star.” The famous rings will be tilted 9 degrees towards Earth and will be visible with high-powered binoculars or small spotting scopes magnifying at least 25 times.
So regardless of exactly how you view Wednesday’s full moon, we at Space.com wish you all clear, moonlit skies.
Joe Rao is an instructor and guest lecturer at New York University Hayden Planetarium. He writes on astronomy for natural history reviewTHE Farmers Almanac and other publications.
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