"the sky shimmered green and blue and red with aurora borealis"

The aurora borealis, also called the northern lights, are natural light displays in the sky, usually observed at night in the northern hemisphere. They are more likely to be seen closer to the North Magnetic Pole. They typically occur in the ionosphere and most often near the equinoxes.

Auroras are caused by the bombardment of solar electrons on oxygen and nitrogen atoms.