Northern lights, or aurora borealis, arise from interactions between the Sun’s activity and the Earth's environment. Here’s the concise picture:

• Source of energy: The Sun emits a stream of charged particles (the solar wind), sometimes in big bursts called coronal mass ejections. When these particles reach Earth, they interact with its magnetic field.

• How they reach the atmosphere: The Earth’s magnetic field guides many of these particles toward the polar regions, where the atmosphere is thin enough for collisions to have visible effects.

• What creates the lights: When energetic particles collide with atoms and molecules in the upper atmosphere (primarily oxygen and nitrogen), they transfer energy to those atoms. As the excited atoms return to their ground state, they emit light, producing the shimmering curtains and rays of the aurora. The colors depend on the type of gas and altitude (green and red from oxygen, blue/purple from nitrogen).

• Where and when you can see them: Auroras are most commonly seen near the magnetic poles, in high-latitude regions. They’re more frequent during periods of strong solar activity and are often best observed on clear, dark nights away from light pollution. The displays can occur any time of year but are generally best from late autumn to early spring in the Northern Hemisphere; similar phenomena occur around the South Pole as aurora australis.

• Typical altitudes: The lowest arc of the aurora is around 80 miles (about 130 kilometers) above Earth, with structures extending higher into the ionosphere.

If you’d like, I can tailor this explanation to a specific location or time of year, or add a simple diagrammatic description of the processes.