The Universe in the ClassroomSign me up!

www.astrosociety.org/uitc

No. 62 - Summer 2003

© 2003, Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112.

Forward the URL for this issue to a friend.

Egg Balancing at the Equinox: Good or Bad Astronomy?

by Phil Plait

Editor's Note: The changing of the seasons. We all experience them and some even look forward to them. Learning and teaching about the how's and why's of them, however, is another story, especially if you live somewhere like San Francisco. Summer is not a time of heat, but of long, cold, foggy days. The reasons for the seasons was tackled in newsletters number 29 and 30 but still many pesky misconceptions persist. One of the more amusing ones is the mysterious ability to balance eggs on end at the Vernal Equinox (curiously, no such claims are made at the Autumnal Equinox). In this issue, Phil Plait, an astronomer who has written a whole book on persistent and prevalent misconceptions and mangling of astronomy takes on this astronomical connection to egg balancing. Is the equinox a time of equality and balance, not just for the division of day and night, but for eggs, as well? Have fun with this issue and then have your students take on this bit of "Bad Astronomy" and debunk it for themselves.

Introduction
The Reason for the Seasons
Combatting Bad Astronomy in Your Classroom
What's really going on?
The origins of the myth
Conclusion

Introduction

This has to be one of the silliest misconceptions around, and it never seems to die. Every year, without fail, some TV station broadcasts a news segment showing local school children standing eggs on end on the first day of spring. Usually, the newscaster will make some vague mention about how this works, but it is rarely specific, and never holds up to too much scrutiny. We'll talk about one typical reason given in a moment, but first, let's look at it from an astronomical angle: what is special about the Spring (also called the Vernal) Equinox that makes it different from any other time of the year?

Axis tilt diagram

The Reason for the Seasons

The Earth's spin axis is tilted with respect to its orbital plane. This is what causes the seasons. When the Earth's axis points towards the Sun, it is summer for that hemisphere. When the Earth's axis points away, you get winter. From the diagram above you can see that the north end of the Earth's axis never points directly at the Sun, but on the summer solstice it points as close as it can, and on the winter solstice as far as it can. (That diagram is taken from Nick Strobel's excellent Astronomy Notes website http://www.astronomynotes.com/nakedeye/s10.htm). Midway between these two times, in spring and autumn, the spin axis of the Earth points 90 degrees away from the Sun. Note that this happens twice a year, in spring and autumn. If you can stand an egg on its end on the Spring Equinox, surely you can on the Autumnal Equinox as well! Yet this always seems to get overlooked. That should be your first indication that something fishy is going on. Also note that the Vernal Equinox is actually heralding autumn in the southern hemisphere. Bad Reader Angela Alexander tells me that the egg myth is also around in Australia, although she admits she may have heard it on the web (which means it could have originated anywhere). Still, it's one more reason to doubt the "truth" behind the legend.

So on the first day of spring and autumn, the Earth's axis happens to be pointing perpendicularly to the direction of the Sun. Although it might seem like a special event, all it really means is that day and night have about the same length: 12 hours each, more or less. Otherwise, it has no real manifestations to us here on the surface; if you were locked in a windowless box (hmmm, sounds like my old office) you would have no way of knowing that it was the equinox. As far as gravity goes, there isn't anything special about this time.

I once heard a newscaster say that you can stand an egg on end during the Spring Equinox because the Sun's gravity "lines up with Earth's". This is just silly: draw a line between the center of the Earth and the Sun, and you'll see that at any time, someplace on the Earth is on that line! If there is any validity to this solar balance claim, then certainly it negates the Spring Equinox claim. I would hope our nation's television journalists would know better. I do a lot of hoping.

Combatting Bad Astronomy in Your Classroom

What I love about this example of Bad Astronomy is that you need not take my word on it. This is one you can prove for yourself!

3 eggs standing

At any day of the year, grab a carton of eggs and try to stand each one. Usually you cannot stand a raw egg because the inside of an egg is a very viscous (thick) liquid, and the yolk sits in this liquid. The yolk is usually a bit off-center and rides high in the egg, making it very difficult to balance. The egg falls over. However, with patience, you can usually make an egg stand up. It may take a lot of patience!

closeup of 3 eggs standing

The pictures you see scattered around here were taken on October 25, 1998 (yes, that's me in that picture). Of course, I could be lying about the date, but again, you can prove this for yourself by trying to stand an egg on end on any random day. Go ahead and try it now! Whenever I buy eggs from the store I grab one or two from the carton and stand them up. It's fun. When the pictures here were taken in October of 1998, I was able to get three eggs standing pretty easily, then my wife helped me stand up five more!

8 eggs standing

| 1 | 2 | next page >>

back to Teachers' Newsletter Main Page