[ELI5] How do we predict solar and lunar eclipse?
In: Mathematics
Orbital mechanics!
While not entirely true, you can imagine the moon and Earth as if they move on rails. Orbits are more or less the same every time, so we’ll treat them like rails (like railroad rails, if you’re unfamiliar with the terminology). Big invisible rails in the sky. They move at speeds which change slightly but the speed always depends upon the height of the rail. We’ve been observing the movement of the Earth and moon for a long time, so even if we didn’t have math to reconstruct these ‘rails’ we would have mapped them out pretty well by now. Since we know where the rails are and how fast the Earth and moon move along their respective rails, all we have to do is calculate when the two will align just right. For instance, the moon’s rail has to line up with the position of the sun when viewed from the Earth’s rail for either kind of eclipse. This will happen twice a year. I can’t really think of an intuitive proof for this without a diagram, alas. However, not only do the rails have to line up, but the moon must also be at a specific point on its rail for a lunar eclipse and the opposite specific point for a solar eclipse.
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