interlude on Lagrange points

promoting this out of my FailBook comments just because

So, there's this diagram which has been making the rounds now that the James Webb Telescope has been launched. It's good at showing where the Lagrange points are and, if you're used to reading topographic maps, what the gravity well generally looks like, that volcano with the 6000 mile deep crater that I talk about here, if you were having trouble picturing that (modulo the small matter that that was all about the Earth-Moon system, and this picture shows Sun-Earth L1-L5; but they both work the same way).

Granted, with L1, most people seem to be clear about the idea that, with Sun and Earth pulling in opposite directions, there's got to be some point in the middle where the forces are cancelling out, even if that's not quite what L1 is. But for L2-L5, people seem to be completely mystified, and I've been seeing far too many wacky attempts at explanations in the last few days.

Time to sort things out:

( Read more... )