00 · IN THREE MINUTES
The answer in three steps
- 1Solar activity supplies energetic charged particles.
- 2Earth's magnetic field guides part of that flow toward polar regions.
- 3Collisions excite atmospheric atoms and molecules, which release coloured light as they relax.
01 · THE GLOW IS MADE LOCALLY
The glow is made locally
The visible light does not travel intact from the Sun. Electrons and ions enter Earth's magnetic environment, and some are accelerated along magnetic field lines into the upper atmosphere.
The glow is made locally
The visible light does not travel intact from the Sun. Electrons and ions enter Earth's magnetic environment, and some are accelerated along magnetic field lines into the upper atmosphere.
solar inputA collision stores energy briefly
Incoming particles collide with oxygen atoms and nitrogen molecules. Those targets enter excited states; when they return to lower-energy states they emit photons at characteristic wavelengths.
particle excitationColour is a clue
Green and red emissions are strongly associated with atomic oxygen, while molecular nitrogen contributes blue, violet and red features. Altitude, density and collision rate change which transitions can survive long enough to shine.
emission spectrumThe oval follows magnetic geometry
Auroras cluster in rings around the magnetic poles rather than the geographic poles. During geomagnetic storms those ovals expand, so displays can become visible much farther from the poles.
magnetic oval02 · A COLLISION STORES ENERGY BRIEFLY
A collision stores energy briefly
Incoming particles collide with oxygen atoms and nitrogen molecules. Those targets enter excited states; when they return to lower-energy states they emit photons at characteristic wavelengths.
03 · COLOUR IS A CLUE
Colour is a clue
Green and red emissions are strongly associated with atomic oxygen, while molecular nitrogen contributes blue, violet and red features. Altitude, density and collision rate change which transitions can survive long enough to shine.
04 · THE OVAL FOLLOWS MAGNETIC GEOMETRY
The oval follows magnetic geometry
Auroras cluster in rings around the magnetic poles rather than the geographic poles. During geomagnetic storms those ovals expand, so displays can become visible much farther from the poles.
Solar activity supplies energetic charged particles.
Space-weather monitors can warn of enhanced activity, but small-scale structure and rapid change prevent an exact street-by-street forecast far in advance.
05 · A STORM IS NOT A SIMPLE SWITCH
A storm is not a simple switch
Solar eruptions can create favourable conditions, but arrival time, magnetic orientation and coupling to Earth's magnetosphere all matter. Forecasts describe probability and intensity, not the path of every curtain.
06 · SOURCES AND EVIDENCE
Sources and evidence
The explanation follows the evidence chain below. Links open the original source.
- 01AuroraINSTITUTIONAL EXPLAINER ↗
Supports a specific claim or evidence boundary used in this article.
- 02AurorasINSTITUTIONAL EXPLAINER ↗
Supports a specific claim or evidence boundary used in this article.
- 03Magnetospheric Multiscale MissionOFFICIAL DATA / TECHNICAL REPORT ↗
Supports a specific claim or evidence boundary used in this article.