The aurora is not a reflection of polar ice, and it is not fire in the sky. It is air glowing where charged particles from the Sun, steered by Earth’s magnetic field, slam into the upper atmosphere. The Sun constantly sheds a wind of plasma. When that wind is gusty, especially after a solar flare or a coronal mass ejection, more particles funnel toward the magnetic poles. Roughly 100 kilometers up and higher, they excite oxygen and nitrogen. Oxygen can shine green or, higher still, deep red. Nitrogen adds blues and purples. The colors are the fingerprints of those gases, the same idea as a neon tube, written on a planetary scale.

Displays follow ovals around the magnetic poles, so Iceland, Norway, Canada, and Tasmania see them more often than cities at mid-latitudes. In strong storms the ovals swell and people farther south get a rare show. The lights move because the incoming particles and the field are not still. They can look like curtains, rays, or a quiet green fog.

Auroras are a reminder that Earth is not sealed. Space weather can also disturb radio, satellites, and power grids. The pretty curtain is a visible edge of a much larger, invisible interaction between a star and a magnetized world. Standing under it is standing at the shoreline of the solar wind.
