There is a superstition that it is possible to stand an egg upright on its end on the date of the equinoxes (and/or solstices). While this is true, it is also possible to stand an egg on its end at any other time of the year. Although this feat is not trivial, a persistent person can usually succeed with enough practice and skill. However, the only connection between success in standing eggs upright and the equinox, to my knowledge, is that because of the superstition, many more people try and persist than would be the case on any other date. Of course, cheating by resting the egg on a thin layer of salt grains and then blowing all but a few invisible grains away is still far and away the easiest method!

Equinox, Solstice