Also known by their Latin name, aurora borealis, the northern lights are visible all across northern Sweden during the dark months of winter. These spectacular displays of green-blue shimmering arcs and waves of light are caused by solar wind, or streams of particles charged by the sun, hitting the atmosphere. The colours are the characteristic hues of different elements when they hit the plasma shield that protects the Earth: blue is nitrogen and yellow-green oxygen. Although the mechanisms which produce the aurora are not completely understood, the displays are generally more impressive the closer you get to the poles – low temperatures are also rumoured to produce some of the most dramatic performances. Gällivare and Kiruna, both well inside the Arctic Circle, are arguably the best places in Sweden to catch a glimpse of the aurora, particularly during the coldest winter months from December to February. Although displays can range from just a few minutes to several hours, the night sky must be clear of cloud to see the northern lights from Earth.