Home on Lagrange

Diagram of Lagrange points, via NASA

I first came across Lagrangian Points many years ago in Arthur C. Clarke’s novel A Fall of Moondust. It boggled my young mind, picturing satellites orbiting in seemingly static positions around the Moon! Of course, in fact they were orbiting Earth and the Moon, affected by and in balance with both gravitational sources. (This is what the best science fiction does: explore scientific concepts, even in passing, within a fictional story.)

This morning, while researching for a project I’m working on, I found myself returning to Lagrangian Points, a phenomenon beautiful in its simplicity.

The American Heritage Dictionary defines Lagrangian Point as:

Any of five points in the orbital plane of two bodies, one of which is much larger than the other, at which a third, even smaller body will remain in gravitational equilibrium. Bodies located at Lagrangian points appear stationary with respect to the larger two bodies.

But that doesn’t really capture the magic.

The Australian Space Academy describes it as:

For any two massive bodies rotating about their centre of mass there exist five ‘stationary’ points where the force on a third small body is zero (in the rotating reference frame).

As my physics teacher would always say, “When it doubt, draw a picture!”

Diagram of Lagrange points, via NASA

But a picture is static, and can capture only so much of something that moves. I found this video animation that I think beautifully illustrates how these Lagrangian Points are stable in motion (if that makes sense). At about 1:05 the animation trails the paths taken by the objects at the Lagrangian Points.

Then there’s this A/V lecture explaining the concept.


And if you really want to get into the nitty gritty, there’s this MIT lecture by J. Kim Vandiver on the physics behind it. (Hello, math, my old friend. Where’ve you been? I hardly know ya.)

In this age, when we’re constantly discovering things we’ve never seen, theorizing things that had never occurred to us, and realizing how much we don’t understand about the universe — a marvelous time — it’s oddly comforting to take in the simple beauty of the Newtonian physics behind these five points of equilibrium.

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Laura Lis Scott is a professional book designer and editor with over 25 years’ experience. She is publisher of Toot Sweet Ink, an independent press. She also provides book design and editing services for independent publishers and authors. You can check out Laura’s book design and editing work at Book Love Space.

As an author, Laura has written for BlogHer, MediaGirl, and corporate clients. She has ghostwritten four fiction books (novellas and novels). Her own fiction has been published in Story Seed Vault and by Toot Sweet Ink. She currently writes science fiction, fantasy, and contemporary fiction.

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