In 1973, there was a total solar eclipse that lasted 74 minutes. Well, sort of -- it was done with a clever trick. Viewed from any spot on Earth, the eclipse lasted a little over 7 minutes, but viewed from a supersonic aircraft flying in the direction of the eclipse, the duration could be stretched out.
The aircraft was a modified Concorde, and it wasn't quite able to keep up with the speed the moon's shadow moved over the face of the Earth. So it couldn't stretch out the length of the eclipse indefinitely. But it was able to stretch it out quite a lot.
This got me curious how fast the moon's shadow moves. For the eclipse we just had, I measured the distance from where it first lands on the North American continent, just south of Mazatlan, Mexico, to where it leaves the North American continent, near Rivière-au-Portage, New Brunswick, Canada, as 4,530 km (metric system!), or 2,815 miles. The time it takes to cross that distance is 1 hour, 27 minutes, 33 seconds. Doing the arithmetic that results in a speed of 3,105 km per hour, or 1,929 miles per hour. Translating that into a mach number we get mach 2.51. The Concorde's maximum speed was mach 2.04. The SR-71 has a maximum speed of mach 3.2, so an SR-71 could in fact keep up with the moon's shadow.
The other question is why eclipses near the equator can last more than 7 minutes while ours are much shorter up here in North America, at around 4 and a half minutes? Apparently the answer to this question is very similar to the supersonic airplane question. The moon's shadow moves from west to east during an eclipse, and the earth itself rotates from west to east as well, in the same direction -- this is why the sun rises in the east. So, the closer you are to the equator during an eclipse, the more the rotation of the earth itself mimics the movement of the supersonic airplane and elongates the eclipse.
