The solar wind, a stream of charged particles moving from the sun's outer corona, is what causes the northern lights.
The magnetic field of Earth works as a shield around the globe, deflecting the majority of solar wind bursts known as solar flares.
However, some particles do enter the upper atmosphere around the poles, where they smash with gas molecules and excite or energize them.
The auroras are created when these molecules undergo another energy loss.
The color of each aurora is determined by the kind of excited molecule and collision altitude.
The most prevalent colors are light yellow and green, caused by oxygen molecules around 120.
Red auroras, which are produced by oxygen about 200 km above the surface and red-purple auroras, which are produced by nitrogen below 100 km, are less common.
As soon as it gets dark, an aurora can be observed if the solar wind is vigorous.
However, the level of activity is subject to rapid change, so monitoring real-time solar activity statistics is your best chance.