The longest eclipse: a 7m31s ceiling, the 743 BC record, Concorde's 74-minute chase
In 1973, a French test pilot pushed a supersonic prototype to Mach 2 to physically outrun the shadow of the Moon, and he stretched a normal eclipse out to 74 minutes. Hey, I'm Salt. I'm Grace. Wait — what? 74 minutes.
Because I thought a solar eclipse was just, you know, a couple of minutes of darkness and then the sun comes right back. Usually, yeah. We actually just had a really short one last week, on August 12th. Right. But they can run longer.
In fact, if you just stand still on the ground, the absolute longest an eclipse can possibly last is a bit over seven and a half minutes. Just over seven minutes. Yeah, seven minutes and 31 seconds. That's the hard theoretical ceiling. It was calculated by this mathematical astronomer named Jean Meeus.
Why is there a hard ceiling at all? Like, what dictates that number? It's, um, it's all just geometry. You need the Earth at its farthest point from the Sun, which astronomers call aphelion, so the solar disk looks as small as possible in the sky. Okay, that makes sense.
And then you need the Moon at its closest point to Earth, its perigee. So the lunar disk looks as big as possible, covering up more of the Sun for a longer stretch. Right, big moon, small sun. Exactly. And then for the final piece, you want to be standing right on the equator.
The Earth spins fastest at the equator, so you're, uh, you're sort of coasting along with the shadow as it sweeps over the surface. Huh. So have we ever actually hit that seven minute and 31 second mark? Not quite. The closest humanity has ever come — at least based on calculations from NASA and eclipse-chasers.
com — was way back on June 15, 743 B. C. You're kidding. No, that one hit seven minutes and 28 seconds over the Indian Ocean. We missed the limit by three seconds, three thousand years ago.
We did. And we won't get that close again for a very long time. Though we do have a good one coming up soon. After that brief one we just had last week, next year, on August 2, 2027, the shadow is going to cross right over Luxor, Egypt. How long do they get for that one?
Six minutes and 23 seconds of totality. Forbes is already calling it the eclipse of the century because it passes directly over the ancient temples there in the Valley of the Kings. The chances of clear skies in the Egyptian desert in August are basically perfect. Wow. That'll be a busy day in Luxor.
It will. It's the longest eclipse left this century. Okay, six minutes is a good run. But it's not seven and a half. When do we actually brush up against that ceiling again?
The projection that gets us the absolute closest is on July 16, 2186. 2186. Yeah. According to Wikipedia's tracking data, that one will pass over South America and last exactly seven minutes and 29 seconds. Just two seconds shy.
Yeah. It's the longest total solar eclipse in a 10,000-year window. But Grace, I want to go back to the top. Because you said a guy got 74 minutes. How is that even possible if the the physics cap it at seven?
Right. So, if the shadow is moving across the Earth, and the planet's rotation caps you at seven minutes, the only way to beat the math is to get in a fast plane and chase it. Well, how fast is the shadow actually moving? It depends where you are, but according to Helioclipse, it's roughly 1,500 miles an hour. Which meant that in 1973, conventional planes were just too, too slow to keep up.
But the Concorde wasn't. Right. The June 30, 1973 eclipse was already a uniquely long one, over seven minutes on the ground in the Sahara. A team of scientists convinced André Turcat — he was the, actually no, he was the chief test pilot for the entire Concorde program — to fly them in the 001 prototype. They used the prototype for an astronomy mission.
They did. They actually cut special portholes into the roof of the fuselage so the researchers could aim their cameras straight up at the sky. Seriously? Yeah, it was a huge modification. So the morning of the eclipse, Turcat takes off from the Canary Islands, he climbs to 55,000 feet, pushes the plane to Mach 2, and basically intercepts the lunar shadow right as it hits West Africa and just just matches its pace perfectly across the Sahara.
Total artificial eclipse. Flying at twice the speed of sound just to keep the Sun blocked out. They stayed in the dark for 74 uninterrupted minutes. They only had to break off and land in Chad because they were running out of land to fly over safely, and Concorde couldn't maintain those speeds over populated areas anyway. That is wild.
Has anyone done it since? Nobody has even come close. The Concorde is retired, and modern commercial jets just don't fly fast enough to pace the shadow. The 1973 flight still holds the Guinness World Record. So unless we build a new supersonic jet, we are just stuck waiting on the ground for 2186 to give us seven minutes.
Basically. We'll, you know, just have to see if technology catches up by then. Thanks a lot for listening to Daybrain.
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