>200 km — red (O)
100–200 km — green (O)
<100 km — blue/violet (N₂)
This 2D cross-section simulator shows the real mechanism behind the aurora: a stream of solar-wind particles sweeps in from the side, and any particle that passes close enough to Earth is captured onto one of the dipole magnetic field lines and guided down toward the pole instead of flying straight through. Each particle's energy decides how deep it can penetrate the atmosphere before it collides and stops, and that stopping altitude sets its colour — high red oxygen emission, mid-altitude green oxygen emission (the classic aurora hue), or low blue-violet nitrogen emission. Raise the solar wind intensity to widen the range of captured field lines and push the auroral oval to lower latitudes, or shift the particle energy to see the dominant colour band move between red, green and blue.