With the sun near its maximum activity this year, many people have been able to witness the beautiful light show calledaurora borealis(northern auroras) oraurora australis(southern auroras). These curtains, streamers, and flickering patterns of light are caused whencharged particlesfrom the sun (mostlyelectrons and protons) hit atoms in the upper atmosphere.

The most common color is pale yellow-green emitted by oxygen atoms below 250 miles altitude (400 km). The classic curtain-shaped auroras are almost always oxygen-green. Sometimes the green curtains show a tinge of red near the tops, also from oxygen atoms.Nitrogen atomscan also emit red light, and rarely it is possible to see a deep blue-violet light from charged molecules of nitrogen.

When an electron or proton from the sun hits an atom, it can knock one of the electrons into a high-energy orbit. When the electron falls back to its normal orbit, it releases a burst of light.