Models have always had the ability to facilitate a greater understanding of the universe. From Aristotle in the fourth century BCE to Iowa City today, physical models of the cosmos and of space phenomena continue to provide a deeper understanding of the world around us, despite the growing popularity of 3D digital modeling and virtual reality.
How were such models used in the past and what do they allow us to do today?
Although polar lights have been around for millions of years, it was not until around 1619 that Galileo would use the term 'aurora borealis' to describe the Northern Lights. Aurora was the Roman goddess of the dawn who crossed the sky in the early morning and Boreas was the Greek god of the north wind. A millenium before Galileo, the Hellenistic philosopher and astronomer Aristotle mentioned in his Meteorologica that there was the shimmering appearance of lights in the sky that he called φάσματα (phasmata).
Polar lights are caused by charged particles in the Earth's atmosphere, mostly electrons and protons, expelled from the Sun in the form of a solar wind. Although an aurora is usually seen by those living at much higher latitudes than Greece or Italy, it is still possible that those in the ancient Mediterranean saw and then sought to explain these phenomena.
Within the Hellenistic Mediterranean, there was already a craze for using models to better understand the cosmos and theorize about how it functioned. The Greek word for the applied art of modeling the cosmos was σφαιροποιία (sphairopoiia). While Aristotle allegedly built a planetarium to model his view of the universe, it was the Sicilian engineer and mathematician Archimedes who set up a mechanized planetarium to imitate the movement of the heavens. His contraption required a number of small metal gears and a chain in order to function.
Two of his astronomical models were apparently taken by the Roman consul Marcellus during the sack of Syracuse, which saw the death of the famed scientist around 212 BCE (Plut. Marc. 19.6). Cicero remarks that he was less than impressed with later seeing one of the Archimedean celestial models that had been deposited in the Temple of Virtue, since the other globe--maintained by the Marcelli family--was of more beauty. Into the late Republic and empire, men like Posidonius and then the Egyptian geographer Ptolemy continued to use models in order to experiment with their celestial ideas and explain theories to their students. Even if many parts of these geocentric models were inaccurate, the astronomers set a precedent for recreating the macro in the micro through the use of physical models.
Into the late 19th century, astronomers and physicists continued to use models to better understand space phenomena, this time with the added technology of electricity. Between 1896 and 1917, a Norwegian physicist named Kristian Birkeland developed a model experiment called the Terrella, which sought to understand the formation of polar lights by drawing electrons onto one sphere from another--imitating the sun and then the creation of an aurora on earth. He did this only after multiple polar expeditions aimed at studying the phenomenon failed and were deemed too treacherous.
In the late 1950s, University of Iowa space physicist James Van Allen would discover that the aurora created toroidal regions--radiation belts later termed "Van Allen belts"--which were conjured when the Earth's atmosphere deflected charged particles. Van Allen described these radiation belts in his handwritten diaries, which are available through a crowd-sourced digital transcription project at the University of Iowa called "DIY History."
A century after Birkeland's original Terrella model and four decades after Van Allen's discovery of radiation belts, a group of CNRS researchers led by Dr. Jean Lilensten at the Institute of Planetology and Astrophysics in Grenoble (IPAG) began to develop a working prototype for modeling auroras and radiation belts within a bell jar with two metallic spheres that could model plasma. This electric model was called a Planeterrella, and would demonstrate the polar lights to students and researchers who were not plasma physicists.
A small number of Planeterrellae now exist across the world. At the University of Iowa, a group of graduate and undergraduate students led by plasma astrophysicist Scott Baalrud modified the blueprint for the model available from the Observatoire Terre Univers Environnement after receiving a grant from the National Science Foundation for a broader research grant. As Prof. Baalrud noted to me, there is increasingly a public component written into almost every science grant that requires research to be made public and accessible in some way. The use of physical models in museums or in exhibits is still a pivotal way that scientists can do public outreach that allows complex ideas to be illustrated to the masses.
Regardless of the rise in 3D digital models or recreations, there is something quite visceral about the continued use of interactive physical models to explain our universe. Videos may be instructive, but as Archimedes would likely confirm, having a tangible model remains one of the best ways to parse astronomical phenomena for the rest of the populace.
Sarah E. Bond is an Assistant Professor of Classics at the University of Iowa. For more on ancient and medieval history, follow her @SarahEBond.