We all know that the compass needle points north because of the Earth's magnetic field, but how exactly does the that field come about?
Geophysicist Dan Lathrop at the University of Maryland wants to find out ... by building his own planet!
His latest effort at the University of Maryland towers over him, a massive stainless steel sphere that looks like a prop from some old science fiction movie. Later this year he plans to fill it with molten metal and set the whole 26-ton ball spinning. At top speed the equator will whirl by at 80 miles an hour.
"It was a little scary the first time we spun it up," he says.