The two things you need to know — and the merger of the two I’ll get to momentarily — are:
1) Tomorrow, Monday, September 22, at 15:44 UT (11:44 a.m. Eastern US time) the Sun’s apparent path in the sky crosses the projected path of the Earth’s equator in the sky. What does that mean? It means that this is the time of the autumnal equinox, the midpoint in time between the summer and winter solstices.
It does not mean you can only stand an egg on end on this day (or on the vernal/spring equinox).
2) APOD is the Astronomy Picture of the Day, the 800 kilogram gorilla of astronomy sites. It’s run by my friends Bob Nemiroff and Jerry Bonnell, and every day they feature an astronomical picture with a brief explanation.
What do you get when you combine (1) and (2)? Why, a picture of me, standing eggs on end back in 1998. That was for the vernal equinox, but what the heck. It’s still a funny picture.
If you want to try to stand eggs on end yourself, I made this handy-dandy video six months ago to show you how.
Happy autumn! And for you Aussies, ¡ƃuıɹds ʎddɐɥ