If you saw the northern lights — either with your own eyes or with the help of your phone — you may have noticed an array of colors. But what causes the different shades of greens, reds ...

The northern lights surprise stargazers by appearing in many forms—from patches or scattered clouds, to streamers, arcs, rippling or dancing curtains. The lights move and change shape and color.

The red line denotes where the northern lights may be visible at the northern horizon, while the colors indicate how likely the occurence of an aurora will be. SWPC map of tonight's aurora forecast.