Did you know that during an equinox you can balance an egg on its end? Try it now or you will lose the moment for another six months!

No its not just an urban legend. I thought it was till I read about it on Sig Lonegren's website Mid Atlantic Geomancy. "Take a raw egg out of the fridge the night before so it warms up to room temperature. On the Equinox, you will find that you can balance the egg on a flat surface, on its fat end. It doesn't work right away (I think it takes time for the yolk to settle), but keep at it, and suddenly, it will feel like it locks, and you can remove your fingers, and it stays there - balanced on its fat end. Honest."

And it does.

The exact moment of the equinox is 4am Saturday 23rd September apparently, but it works for a day or so either side.

Can any one of a scientific nature tell me why? Or even tell me of an ancient Celtic myth (or Egyptian, maybe) that explains it?