The Aurora Borealis are the result of interactions between the Sun and Earth's outer atmosphere. The Aurora Australis is the southern hemisphere counterpart to the Aurora Borealis.
The sun emits electrically-charged particles called ions, which move away from the sun in a stream of plasma which is comprised of ionized gas. This plasma flow is known as the solar wind. As the plasma comes in contact with the Earth's magnetic field, the ions are agitated into moving around the Earth. Some of the ions become trapped and will interact with the Earth's ionosphere causing the ions to glow.
The color of the aurora depends on which gas is being excited by the electrons and on how much energy is being exchanged. Oxygen emits either a greenish-yellow light (the most familiar color of the aurora) or a red light; nitrogen generally gives off a blue light. The oxygen and nitrogen molecules also emit ultraviolet light, which can only be detected by cameras designed to record ultraviolet light.
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