What Is an Aurora?

The Sun continuously emits a stream of charged particles called the solar wind. When these particles reach Earth, most are deflected by the magnetosphere, but some funnel along magnetic field lines toward the poles. As they collide with oxygen and nitrogen molecules in the upper atmosphere (80-300 km altitude), the gas molecules become excited and release energy as photons of light. Oxygen produces green and red glows, while nitrogen contributes blue and purple hues. Auroras are visible near the magnetic poles — aurora borealis in the north and aurora australis in the south.