Here’s a dazzling picture of the Aurora Borealis being simulated on a terrella. A terrella is not much more than a magnet that’s been carved into a ball, but it has helped scientists both visualize and prove points about the Earth and its magnetic field.
The first terrella was carved back in Elizabethan times, when people wanted to know what the movement of a magnet on a compass indicated about the Earth. William Gilbert – Royal doctor and earliest known incarnation of Bill Nye the Science Guy – thought it was because the Earth was a huge magnet, and made a magnetized mini-Earth to show that he was right. A compass that moved over the so-called terrella moved the way a compass did over the surface of the Earth.
The picture up top is a recreation of a series of experiments done in the late 1800s and early 1900s, by Kristian Birkeland, attempting to explain the phenomenon behind the polar aurora. Birkeland, instead of carving his terrella directly out of a magnet, put an electromagnetic coil inside a metal sphere. He then put the sphere in a vacuum chamber and released a just a bit of gas between it and the metal plates he suspended it between. The gas mimicked the Earth’s atmosphere. When he shot electrons at the terrella – imitating the solar wind – the magnetic field of the terrella steered the electrons towards the poles, where they excited the gas molecules until they glowed. Anyone could see the similarities between this and the Northern Lights.
Birkeland tried other experiments as well, attempting to model phenomena such as sunspots and solar flares, and their effects on Earth. He was not as successful with this as he was with the auroras. When computers came along, no one needed the poor terrella anymore. It’s still pretty, though.
