American Scientist

What causes auroras?

Solar winds send charged particles from the Sun into Earth’s magnetic field, where they follow Earth’s magnetic field lines. At the poles, where the lines intersect with Earth’s atmosphere, these particles create auroras.

The charged particles collide with atoms and molecules in Earth’s atmosphere, sending them into an excited state. The atoms and molecules then emit colored light as they release the extra energy and return to their ground state.

In the Northern Hemisphere, the effect is known as the northern lights or aurora borealis. In the Southern Hemisphere, it is called the southern lights or aurora australis.

Where can you see auroras?

Usually, auroras are visible only at extreme northern or southern latitudes. However, they can be viewed outside of the usual auroral zone during periods of high solar activity.

What causes the different colors?

The colors of auroras are caused by the collision of charged particles, usually electrons, with different gases at varying altitudes.

Rosy hues are caused by the excitation of oxygen atoms at high altitudes. Red auroras are rare and are seen only during intense solar activity.

Green auroras are the most common. They are generated by oxygen atoms at middle altitudes, where oxygen concentration is higher and more energy is lost to collisions.

These cool tones result from the excitation of nitrogen molecules at low altitudes. As with red auroras, these colors appear most often during intense solar activity.

Shades of yellow and pink appear in the sky when different colors of auroras combine, most often during periods of high solar activity. Excited oxygen and nitrogen atoms in the atmosphere also emit ultraviolet light, which is not visible to the human eye.