What Are the Polar Aurorae?

Polar lights (aurorae) have been described since Antiquity. Aristotle and Pliny wrote about the fear triggered by the arctic aurora, which people thought to forecast great adversities. Often, these red lights were taken as coming from a large fire. During the Roman emperor Tiberius, Roman cohorts run to save the Ostia fortress, believing it was burning. During the 18th century, Danish guards of Copenhagen took an Arctic Aurora as the sign the city was in flames and triggered the alarm.

The polar aurorae are produced by the impact of electrons emitted by the Sun with the atmosphere of the Earth, rarefied at high latitudes. Colliding with the atoms in the atmosphere, the solar electrons emit energy translated through polar lights. The phenomenon occurs at the two poles because the magnetism of the Earth deviates the flow of the electrons came from the Sun, attracting them along the terrestrial magnetic field towards a pole or another.

The polar lights appear mostly in two forms. One type appears like wide rainbow arches, that last at the horizon for hours and even days. The second type is much more spectacular through the variety of shapes and color intensities. The most frequent of these aurorae appear like curtains floating in the atmosphere. They look crumbled on the edges but their colors are extremely beautiful.

They appear like drags of brown light, over which raises a curtain of violet clouds, thin enough for the stars to be seen through it. The center is always a bright yellowish, which grows continuously, like a rainbow. The edges appear like reddish and greenish stripes. They unfold like multicolor flags, fluttering like blown by the wind. The bunches of colors move from one place to another until they resemble large pyrotechnic fires. The colors are extremely varied and change at the same time. Various hues of red, orange, yellow and green mix. The sky appears like a fire cupola whose lights agitate like sea waves. The color intensities change like in a sunset. When the aurora starts to shut off, the red color remains the last, blooding the sky.

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