It's considered polite to nod at someone passing by. But this is a
human behavior, so what is the earth nodding at? Whatever it is, it has a profound
effect on humans. OK, getting down to brass tacks, what do we mean, the earth is
nodding, and why should that affect us? Well, if the pathway the earth takes around the
sun were a flat table and the earth set upon it, the axis around which the earth spins
would be at an angle instead of standing up straight. Furthermore, if you could watch
it over thousands of years, the departure from straight up and down--the nodding--would
vary from about 22 to 25 degrees. So, how does this affect us? Simple! If there was no
tilt, there'd be no seasons in our desert, and the more the tilt, the stronger the
seasons. Currently, the earth is on its way to standing more upright, with less
seasonality. Just don't hold your breath, though--it takes about 41,000 years to go
through a whole cycle!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.