What Causes the Aurora Borealis ?

The aurora appears as a curtain, an arc or a spiral, usually following the lines of Earth’s magnetic field. Most displays are green, but strong occurrences can be red, violet, and white. For most of human history, the colors were a source of mystery. Northern cultures created legends about the lights, often associating them with life after death. The Inuit believed the spirits of their ancestors were dancing across the sky, and in Norse mythology, the aurora was a bridge of fire connecting the gods to the heavens. But by the 1880s, scientists suspected a connection between the northern lights, as they are also known, and the Sun.

The temperature above the surface of the Sun is millions of degrees Celsius, causing frequent and violent collisions among gas molecules. Electrons and protons thrown free by the collisions hurtle outward from the Sun’s rotation and escape through holes in the magnetic field. Solar wind carries the charged particles, most of which deflect off Earth’s magnetic field. However, near the North and South Pole, the magnetic field is weaker, allowing some particles to enter the atmosphere. When the charged particles from the Sun strike the atoms and molecules in Earth’s atmosphere, they excite those atoms. An excited atom is one whose electrons move to high-energy orbits, and in the process the atom releases a particle of light, or photon. Different gases in the atmosphere give off light of different colors. Oxygen causes a green display and nitrogen produces red or blue colors. We perceive the collisions between solar particles and atmosphere gases as the northern lights. Many tourists trek to the northern and southern poles of Earth to catch a glimpse of the auroras, now considered one of the seven wonders of the natural world. And even though science can explain the oncemysterious phenomenon, the dazzling display of lights still provokes magical thoughts of dancing ancestors and bridges to the world beyond.

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