Astronomy — Auroras
- The Sun constantly sprays the solar system with millions of tons of charge particles each minute. Particularly energetic surface events such as solar flares greatly increase the number and energy of the charge particles shot out from the Sun.
- Like the Earth, the Sun also has a magnetic field, although in its case, the field fills the entire solar system. Scientists call this the interplanetary magnetic field. The protons and electrons ejected by flares are propelled away from the Sun and follow these interplanetary field lines. Inevitably, a small percentage of the particles encounter Earth’s magnetic field. Since the electron carries a negative electrical charge and the proton a positive charge, the two particles behave differently when they encounter Earth’s magnetic domain, or “magnetosphere.” Like an enormous sorting machine, the magnetic field separates the protons from the electrons. as they pass into the magnetosphere.
- Forcing the electrons and protons apart in this manner creates an electric potential. It’s just like pulling laundry apart after taking it out of the dryer. In this case, your fluffy sweater acquires a positive charge (an excess of protons) while the old sock acquires a negative charge (an excess of electrons). The difference in charge between the two bits of clothing creates an electric potential which can be demonstrated when you bring the two close together. The two pieces are attracted to each other, the infamous “static cling.” As the two meet, a current of electricity (free-flowing electrons) passes from one to the other.
- In Earth’s magnetosphere the separation of the protons and electrons creates an electric potential of between 20,000 and 150,000 volts. This turns the magnetosphere into an enormous battery, storing the electric energy it has received from the solar wind. Some current is always flowing along Earth’s magnetic field line, but on some occasions the stored energy is released in a burst. When the magnetic field lines channel the energy into the atmosphere, we get aurorae. The question is, what triggers the release of the stored potential? The answer is currently a topic of energetic debate.
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