Aurora (astronomy) - History of Aurora Theories

History of Aurora Theories

Multiple superstitions and obsolete theories explaining the aurora have surfaced over the centuries.

• Seneca speaks diffusely on auroras in the first book of his Naturales Quaestiones, drawing mainly from Aristotle; he classifies them ("putei" or wells when they are circular and "rim a large hole in the sky", "pithaei" when they look like casks, "chasmata" from the same root of the English chasm, "pogoniae" when they are bearded, "cyparissae" when they look like cypresses), describes their manifold colors and asks himself whether they are above or below the clouds. He recalls that under Tiberius, an aurora formed above Ostia, so intense and so red that a cohort of the army, stationed nearby for fireman duty, galloped to the city.

• Walter William Bryant wrote in his book Kepler (1920) that Tycho Brahe "seems to have been something of a homœopathist, for he recommends sulphur to cure infectious diseases “brought on by the sulphurous vapours of the Aurora Borealis."

• Benjamin Franklin theorized that the "mystery of the Northern Lights" was caused by a concentration of electrical charges in the polar regions intensified by the snow and other moisture.
• Auroral electrons come from beams emitted by the Sun. This was claimed around 1900 by Kristian Birkeland, whose experiments in a vacuum chamber with electron beams and magnetized spheres (miniature models of Earth or "terrellas") showed that such electrons would be guided toward the polar regions. Problems with this model included absence of aurora at the poles themselves, self-dispersal of such beams by their negative charge, and more recently, lack of any observational evidence in space.
• The aurora is the overflow of the radiation belt ("leaky bucket theory"). This was first disproved around 1962 by James Van Allen and co-workers, who showed that the high rate of energy dissipation by the aurora would quickly drain the radiation belt. Soon afterward, it became clear that most of the energy in trapped particles resided in positive ions, while auroral particles were almost always electrons, of relatively low energy.
• The aurora is produced by solar wind particles guided by Earth's field lines to the top of the atmosphere. This holds true for the cusp aurora, but outside the cusp, the solar wind has no direct access. In addition, the main energy in the solar wind resides in positive ions; electrons only have about 0.5 eV (electron volt), and while in the cusp this may be raised to 50–100 eV, that still falls short of auroral energies.
• After the Battle of Fredericksburg the lights could be seen from the battlefield that night. The Confederate army took it as a sign that God was on their side during the battle. It was very rare that one could see the Lights in Virginia.