Legend has it that during the equinox (specifically the vernal, or spring, equinox) special conditions exist that allows for an egg to balance perfectly on its end. It is implied also that only during the equinox is it possible to achieve this balance.
So is it possible to balance an egg on its end during the equinox? Well, yes!
However, there is nothing special about this feat. In fact, it is possible to balance an egg on its end any day of the year. All that you need is a hard flat surface.
All that it takes is a steady hand and some practice, though I will say that it is not easy at first. It is even possible to balance an egg on the narrower end, though this requires even more patience.
How Did The Myth Get Started?
The origins of this myth are attributed to stories that the ancient Chinese would create displays of eggs standing on end during the first day of spring. Eventually news of this lore spread over to the western world.
This sparked a rash of news stories that sought to test the theory and challenged people to try standing eggs on their end during the spring equinox, the first day of spring in North America. Of course, some were successful and word of this power spread.
Never mind the fact that there were two problems with this little experiment. First of all the ancient Chinese celebrated the first day of spring about six weeks earlier than the equinox, meaning that the recreation of this event wasn't even on the correct day.
Secondly, almost no one (at least affiliated with the media anyway) did the scientifically responsible thing and re-ran the experiment on a day other than the equinox. If they had they would have found that it was still possible and that there was nothing special about the equinox.
While this myth has been debunked by scientists and curios laymen the world over, there are still those every year that promote it. In fact many local news outlets yearly run stories and show videos of school children attempting the balancing act. And of course since at least one of the children (or whoever) is going to eventually get it to work the myth is further reenforced.
How Does it Work?
So if the equinox has nothing to do with why an egg will balance on its end, then what is the reason? Er, yeah, good question. The fact is that this is not entirely clear.
Many believed that it had to do with the small bubbling that exists on the fatter end of the egg. That these little bumps acted like little legs that helped prop the egg up.
However, it is possible, as I mentioned earlier, to balance an egg on the skinny end as well and there are almost never any bumps on that end.
There are theories abound that it has something to do with the structure of the egg, either internal or external. But no one has been able to offer a sufficient explanation as to how this would be the case.
In short, we really don't know. It probably has something to do with how the egg is shaped, coupled with the internal structure of the egg allowing it to remain in balance. But at this point, it is anyones guess.