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The New Black Supermoon On Friday Will Make A River Go Backwards

On Friday, August 30, the moon will be almost simultaneously “new” and get almost as close to Earth as it ever does. Its influence on our tides will be especially strong, and that, combined with the influence of the Sun on the same side of Earth, will result in powerful “king” tides that will mean high tides … and even force one river to flow backwards.

In terms of moon-gazing, it’s nothing you can see or observe, so don’t bother going outside to take a look, though its effects will certainly be visible. So what is a “New Black Supermoon?” Here’s everything you need to know.

On Friday, August 30, the moon will reach perigee just five hours past its fleeting New Moon phase. It will happen at 15:58 UTC (16:37 a.m. BST, 11:37 a.m. EST and 8:37 a.m. PDT). At that point it will be 357, 176 km from Earth, which is the closest it has been to Earth since February’s supermoon. It may not be the closest moon of the year, but the “New Black Supermoon” is the closest “New Moon Supermoon” of 2019.

The sun and moon both influence the height of the tides, but when they’re on the same side of Earth, that influence is greater. During every New Moon, the sun and moon work together, but when the moon is closer than usual–as it is on Friday–it causes a “perigean spring tide.” The sun and moon’s combined gravitational impact is greater, so the range between low tide and high tide is also greater. That fact that the point of New Moon and the point of perigee are so close together is what’s decisive.

That would be the River Severn in the U.K. known as the “Severn Bore,” the phenomenon occurs because this mighty river spills-out into the narrow Bristol Channel. A tidal bore is when a wave travels up a river in the “wrong” direction, against the current. Here, the tidal range is the second highest in the world and it’s common for a wave to flow backwards. However, only just after a supermoon is it possible to see a 10 meter+ wave. After 20:45 BST (exact timings for various locations are here) on Saturday, August 31–the day after the New Black Supermoon–a 10.1-meter wave is expected to surge up the River Severn. It will be sight and sound to behold, though it often brings flooding to parts of Gloucestershire.

So while it may not be visible itself, the effects of the “New Black Supermoon” make it arguably more important to know about that purely visual spectacles like a moon with a great name (like January’s “Super Wolf Blood Moon Eclipse”). Besides, should we define astronomical events according to whether we can see them or not? Of course we shouldn’t. Next up in 29 days is a “secret supermoon” on September 28 that will lead to an even bigger tidal bore.