The charged particles causing the aurora are guided by Earth’s magnetic field and therefore enter the atmosphere in a ring around each magnetic pole, referred to as the auroral oval. This oval expands and contracts considerably in response to varying solar wind conditions, but there’s always aurora somewhere. During quiet periods it is faint, however. The map below shows the probability of observing aurora on a dark, clear night.
A trickier question is where the aurora can be seen most often. Then you need to take weather into account, a problem we’ll be looking at in the aurora travel guide.