The sturgeon living in the Great Lakes don’t have a lot to do with the moon—or at least they didn’t until the Algonquin Native American tribe came along. The Algonquins discovered that sturgeon were most plentiful in the lakes in August, and so they paid a small tribute to that fact. When a full moon appeared in the sky in that month, they dubbed it a sturgeon moon. But it wasn’t just any full moon that would earn the honorific. It had to be a so-called supermoon—one of which will occur today, Aug. 1.
Supermoons are striking cosmic spectacles, and they occur because of the nature of the moon’s orbit around the Earth. On average, the moon is 384,400 km (238,855 mi.) from Earth—but that number changes. The moon’s orbit is not circular, but elliptical. At its closest approach, or perigee, it is 363,300 km (226,000 mi.) from us; at its furthest remove, its orbit carries it 405,500 km (253,000 mi.) away. A supermoon occurs when two things coincide: the moon is full, and it’s also at perigee. Together, those factors make the moon appear 30% brighter and 14% larger than it usually does. The spectacle is greatest when the moon is close to the horizon as opposed to high overhead, because, in a bit of cosmic optical illusion, its proximity to smaller surface features like houses and trees makes it appear bigger still.
The U.S. will not be the best place from which to see today's Sturgeon moon, which will reach its peak illumination at 2:39 p.m. EST. Viewers in the Eastern Hemisphere will get a far better view. But by nighttime in the U.S. the moon will still be in the sky, easily—and beautifully—visible by looking to the southeast.
Supermoons have become more common than they used to be—but not because the moon has gotten any closer to the Earth. Rather, it’s that astronomers, as well as NASA, have changed the standards of what constitutes a supermoon, defining it as a full moon that comes within 90% of perigee, rather than requiring it to reach that closest 226,000 mi. approach.
Still, looser definition or not, 2023, is a good year for supermoons, with four of them appearing. There was the Full Buck supermoon on July 3—another Native American name, chosen because July is the time of year male deer grow their antlers. There is today’s Sturgeon moon. On Aug. 30, there will be a Blue supermoon—“blue” being the name given to any full moon, super or not, that is the second in a month. Finally, on Sept. 28 will come the Full Corn supermoon, yet another Native American name, chosen because September is corn harvesting season. Next year, the sky will be stingier with its supermoons, with only two occurring—on Sept. 18 and Oct 17.
Hard as it is to resist the sight of a supermoon, not everybody is so smitten with them. In 2017, astrophysicist, author and television personality Neil DeGrasse Tyson famously tweeted, “If last month’s full moon were a 16.0 inch pizza, then this month’s ‘Super’ Moon would be 16.1 inches. I’m just saying.”
But Tyson—his astrophysicist bona fides not withstanding—is in a small minority on this one. The moon had a cataclysmic origin—the result of a collision between Earth and a passing planetesimal 4.5 billion years ago. But if the moon was born in violence, it lives in loveliness—never more so than on a night like tonight.
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Write to Jeffrey Kluger at email@example.com