The Sun supplies a changing flow of energy
The Sun continuously releases the solar wind, a plasma made mainly of charged particles carrying a magnetic field. The flow is always present, but its speed, density and magnetic structure vary. Coronal holes can feed faster streams, while coronal mass ejections can send large magnetic structures through interplanetary space.
Not every change at the Sun produces an aurora display at Earth. The disturbance must reach and interact with our planet's magnetic environment, and its orientation can matter as much as its speed. That is why a bright solar flare seen from Earth is not, by itself, a forecast of northern lights.
Earth’s magnetosphere redirects the interaction
Earth's magnetic field dominates a region of space called the magnetosphere. The solar wind compresses its sunward side and stretches a long tail away from the Sun. Energy can enter and accumulate in this system when the solar-wind magnetic field couples effectively with Earth's field.
The magnetosphere is not a solid shield. It is a dynamic plasma environment. During geomagnetic activity, stored energy and particles can be reorganised and accelerated. Magnetic field lines guide many of those particles toward the upper atmosphere at high geomagnetic latitudes.
Atmospheric collisions make light
Aurora becomes visible when energetic particles, usually electrons, collide with atoms and molecules in the upper atmosphere. Those collisions raise oxygen or nitrogen to excited energy states. As the gases return toward lower-energy states, they emit photons. The result is a glow rather than sunlight reflecting from a cloud.
The colour depends on the gas, altitude, particle energy and atmospheric conditions. Oxygen commonly produces green and can produce red at higher altitude; nitrogen contributes blue, purple and pink emissions. These are physical emission processes, but a camera and the human eye can record their colours differently.
Why aurora forms an oval
Particle entry is organised around Earth's magnetic poles, so aurora commonly forms rings called auroral ovals rather than sitting exactly over the geographic poles. The oval changes shape, position and intensity as the magnetosphere responds to the solar wind.
During quieter conditions the visible oval is usually confined farther poleward. Strong geomagnetic disturbances can expand it toward lower geomagnetic latitudes. An observer can sometimes see an active oval on the poleward horizon even when the brightest activity is not directly overhead.
Turning physics into a viewing decision
Space-weather activity is only one part of seeing aurora. The sky also needs to be dark enough, cloud can block the view, moonlight can reduce contrast, and local light pollution or terrain can matter. A current auroral oval should therefore be read alongside local sky conditions.
GreenHalos keeps those factors separate and links the short-range operational picture to NOAA SWPC. Its visual layer is GreenHalos processing of source data, not a photograph and not an official NOAA product. Use the live globe as a current activity guide, then verify darkness, cloud and an unobstructed viewing direction.
Evidence register
Primary sources
Sources were checked on . Each record identifies which sections it supports.
- Auroras NASA Science Supports: The Sun supplies a changing flow of energy; Atmospheric collisions make light; Why aurora forms an oval
- Aurora Tutorial NOAA Space Weather Prediction Center Supports: Earth’s magnetosphere redirects the interaction; Turning physics into a viewing decision