Every six months, almost like clockwork, I hear someone repeat the same bit of science wisdom: “It’s the equinox; today you can balance an egg on its end.”
“Oh, and why is that?” I answer coyly, salivating in anticipation of the scrambled-up science omelet I’m about be served. The answer is generally vague and slippery. “Well, the earth and the sun are lined up today…and, um…their gravity is balanced.”
Equinox, in case you have been living under a rock on the third rock from the Sun, occurs twice a year—on the two days in which the earth’s axis of rotation is pointed neither toward nor away from the Sun—on or near September 22 and March 22.
Now that we are safely past the equinox by a few days, I encourage you to drop the extremely important stuff you are clearly doing and have a go at balancing an egg on its end today. If by some chance you manage to do it—keep trying, you’ll get it—you’ll have reason to suspect that the calendar has little to do with your success.
Any object, ovoid or otherwise, balances when its center of gravity is located directly over its base of support. An egg has a smallish base, to be sure, but a closer look reveals a surprisingly unsmooth, almost lunar surface, with craters and bumps that function like tiny tripods to help prop it up. What role is played by seasonal shifts in the gravitational field? Goose egg, my friend.
The seemingly indestructible myth of the seasonally stand-up egg was inadvertently hatched by a 1945 Life magazine article that described a Chinese tradition of egg-balancing on the first day of spring. What the article failed to mention was that, by the Chinese calendar, the first day of spring falls in early February—six weeks before the spring equinox.
So go on, go find an egg and try it. Balance is beautiful, on any day of the year.
The pitted surface of a chicken egg, viewed with a scanning electron microscope (SEM). Image courtesy of Jettie van Lanschot, School of Conservation, Denmark.