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Spectacular Auroras

The most spectacular manifestation of the connection between the Sun and the Earth is the Aurora Borealis (Northern Lights) and the Aurora Australis (Southern Lights). For millennia, people have watched them and worried about what ill portents they were heralding. It wasn't until the mid-1800s that scientific studies began to uncover many of their mysteries.

Scientists learned that aurora often accompanied magnetic 'storms' and an unsettled magnetosphere; they were produced by flows of charged particles entering the atmosphere; they came and went with the sunspot cycle; and their colors were the product of excited oxygen and nitrogen atoms hundreds of miles above the surface of the Earth.

By the turn of the 20th century, scientists actually created artificial aurora in their laboratories, and once television and the fluorescent lamp were invented, it was pretty clear just how aurora worked. What scientists still didn't understand was what was triggering them. Some thought it was from direct currents of particles from the Sun itself. Others felt it was more complicated than that.

Thanks to intensive study by research satellites during the Space Age, aurora have been substantially de-mystified, even as their ethereal beauty has remained to dazzle us and inspire awe. When the magnetism of the solar wind is the same as the south-type polarity in the daytime side of the Earth, an invisible valve opens in the magnetotail region, allowing particles and energy to penetrate deep into the magnetosphere.

In the delicately balanced magnetic tail of the Earth, magnetic fields can become crossed just as in solar flares. The energy stored in the magnetic field can be liberated as currents of charged particles.

These accelerated particles flow into the equatorial regions of near-Earth space and become trapped in the ring current. Positively charged particles drift westward while negatively charged particles drift eastward. In a process scientists don't fully understand, some of these particles also flow along the magnetic field into the polar regions. There, these million-ampere currents cause the spectacular displays we see as aurora, and the currents that cause them also heat the atmosphere and ionosphere.

Source:NASA

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