Auroras appear when charged particles from the Sun strike gases high in our atmosphere.

The longer version

Auroras glow when energetic particles carried by the solar wind are funneled by Earth's magnetic field toward the poles. Collisions with oxygen and nitrogen high in the atmosphere excite those atoms, and the light released as they settle back down produces the familiar curtains. The displays typically appear tens of kilometers above the ground.

Different gases and altitudes give different colors, with green and red from oxygen and blue or purple tones from nitrogen. Activity intensifies when the Sun releases bursts of particles toward Earth. Similar displays occur on other planets that possess both a magnetic field and an atmosphere.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.