Total solar eclipses along the path of totality are one of the most breathtaking sights in nature. Day turns into night as the moon slides perfectly in front of the sun — and for a few brief minutes, viewers can even see prominences, giant eruptions of plasma arcing off the sun's surface, normally impossible to see with the naked eye.
It's one of the most breathtaking sights in nature — and it only works because of a wildly precise "coincidence" of size and distance. Here's what makes it work:
A perfect size ratio. The sun is about 400 times wider than the moon. Line up 400 moons side by side, and they'd stretch across the sun's diameter.
A matching distance ratio. The sun also happens to be about 400 times farther from Earth than the moon is. Two completely unrelated numbers — one about size, one about distance — landing on almost the exact same ratio.
The same apparent size. Because those two ratios match, the sun and moon appear nearly identical in size from Earth — even though one is a small rock and the other is a massive star.
A narrow window. The moon's orbit isn't a perfect circle, so its distance from Earth varies slightly. If it's a bit farther away during an eclipse, the moon can't quite cover the sun, leaving a bright "ring of fire" instead of full darkness. The overlap that produces a total eclipse is a tight one.
Two entirely unrelated numbers — size and distance — line up close enough to give us one of the most spectacular sights available anywhere in the solar system.
