Aurora polaris

An aurora polaris was a captivating appearance of strange, undulating lights in the sky on cold, clear nights in the polar regions of worlds such as Toril. Near the northern poles, these were called northern lights.

Description
Aurorae had a wide range of shapes—curtains, halos, pillars, streaks, whisps—and a plethora of colors—usually pale green or pink but also shades of red, yellow, blue, or violet.

Aurorae usually lasted from one to six hours and provided a similar amount of light as the moon.

Learned scholars knew that the auroral displays were actually roiling regions of intense electrical energy some six to nine miles (ten to sixteen kilometers) above the surface, able to harm any creature that might be able to fly to such heights.

Reputation
The inhabitants of the divine realm of Asgard, located on the plane and layer of Ysgard according to the Great Wheel cosmology, believed that an aurora polaris was a reflection of fallen warriors still fighting in the afterlife. Many travelers of the Deep Ethereal likened the appearance of ethereal curtains to the northern lights.