Tonight, at 11:03pm Central Daylight Time, fall officially arrives for the northern hemisphere, and spring arrives for the southern hemisphere. At that instant, the apparent position of the sun in the sky crosses the equator, heading south for the winter (along with birds and many retirees).
Those of you who look at sunset/sunrise times may notice that today is not exactly twelve hours from sunrise to sunset, as you would think should happen, since the term "equinox" means equal night and equal day. This would be true if Earth didn't have an atmosphere, but our atmosphere bends light so that the sun appears to rise earlier and set later then it actually does.
By the way, the legend about being able to balance an egg on its pointy end only on the equinox is just a legend. With patience, you can do that trick any day of the year. And, if you don't want to be patient, trying to balance the egg on top of a tiny pile of salt or sugar will help you a lot.