How the Aurora Works
The northern lights look like magic, but they follow a clear chain of physics — from a storm on the Sun to glowing curtains 100 kilometres above your head. This friendly guide walks the whole path, explains the colours, and shows you how to read a real space-weather forecast.
Open the live tracker →From the Sun to the sky: the chain of events
Every aurora starts with the solar wind — a constant stream of charged particles blowing off the Sun at roughly 300–800 km/s. That wind carries the Sun's own magnetic field with it. When it reaches Earth, it slams into our magnetosphere, the protective magnetic bubble that shields the planet. Most of the time the wind simply flows around us. But when the field embedded in the wind points south (a negative Bz), it links up with Earth's own field and opens a channel for energy to pour in.
That energy loads the magnetosphere's long night-side tail like a stretched elastic band. When it snaps back — a process called magnetic reconnection — it flings particles down along the magnetic field lines toward the poles. Those field lines funnel the particles into two rings around the magnetic poles: the auroral ovals. Where the particles finally crash into the upper atmosphere, the air lights up. Bigger, faster, more southward-pointing solar wind means the oval swells outward and the show slides toward lower latitudes.
Why the aurora glows — and where the colours come from
The light itself is the atmosphere fluorescing. Incoming electrons collide with gas atoms high above the ground and knock them into an excited, higher-energy state. A moment later each atom relaxes and releases that energy as a photon — a tiny flash of coloured light. The colour depends on which gas is hit and how high up it happens, because the thin air at the top lets atoms glow in ways the denser air below cannot.
Green — oxygen
The classic curtain colour, from oxygen around 100–150 km. It is the most common because oxygen is abundant and our eyes are very sensitive to green.
Red — oxygen (high)
Above ~200 km the air is so thin that oxygen glows deep red. This crimson tops the tallest, most energetic displays.
Blue & purple — nitrogen
Nitrogen molecules add blue and violet fringes, usually along the lower edge of a bright, active arc during strong storms.
Height, 100–300 km
The whole display lives well above aircraft and weather — roughly 100 km at the base to 300 km at the red top.
So a tall, storm-time aurora can stack green over red over blue in a single frame — each band is a different gas at a different altitude reacting to the same rain of particles.
Where and when to look
Aurora is easiest under the auroral oval, so the far north — northern Scandinavia, Iceland, Alaska, northern Canada — sees it on many quiet nights. Everyone else waits for a geomagnetic storm (graded G1 to G5) to expand the oval southward. Three practical rules cover almost everything a beginner needs:
Go dark. Light pollution is the aurora's biggest enemy — drive away from town and give your eyes 15–20 minutes to adapt. Go late. Activity often peaks in the hours around local midnight, when your patch of Earth swings under the most active part of the oval. Go clear, and face the pole. You need a cloud-free sky and an open northern horizon (southern, if you are below the equator). A camera helps enormously: a phone's night mode or a few-second exposure will catch faint colour your eyes read as grey. Check whether tonight is worth it and glance at the aurora map before you commit to the drive.
Reading a forecast: a mini glossary
Space-weather dashboards throw a lot of numbers at you. Here is what actually matters, in plain language, so a forecast stops looking like a wall of jargon.
KP index (0–9)
A global 0–9 scale of geomagnetic activity. Far north can see aurora at KP 2–3; mid-latitudes usually want KP 5+. KP index →
Bz
The north–south tilt of the incoming magnetic field. Southward (negative) Bz is the master switch that lets energy in. Bz explained →
Solar wind speed
How fast the particle stream arrives, ~300–800 km/s. Faster wind hits harder and lifts your chances. Solar wind →
L1 & the oval
Spacecraft at the L1 point, ~1.5 million km sunward, measure the wind ~30–60 min before it reaches us — an early warning for the auroral oval. Space weather →
Aurora basics FAQ
Do I need a solar storm, or can I just get lucky?
It depends entirely on your latitude. Under the auroral oval — think Tromsø, Reykjavík or Fairbanks — quiet nights at KP 2–3 are often enough. The farther from the poles you live, the stronger the geomagnetic storm you need to pull the oval down to you, which is why mid-latitude sightings usually coincide with a G2–G3 event. Watching a live aurora forecast tells you which case you're in tonight.
Why does the camera see colours my eyes miss?
Human night vision runs mostly on rod cells, which are sensitive to light but nearly colour-blind, so a faint aurora often looks pale grey or white to the eye. A camera gathers light over a multi-second exposure and records colour the whole time, so green and red pop out that your eyes simply can't register in real time. This is normal — the aurora really is there; your sensor is just more patient than your retina.
Are the northern and southern lights the same thing?
Yes. The same particles funnel into both magnetic poles at once, producing the aurora borealis in the north and the aurora australis in the south as near-mirror images. They tend to brighten and fade together because they're driven by the same solar-wind conditions — the same Bz, the same geomagnetic storm. The southern oval is just harder to watch because so much of it sits over open ocean and Antarctica.
Put the theory to work tonight
You know the chain now — solar wind, southward Bz, an expanding oval, glowing oxygen and nitrogen. See it all as live numbers with a single 0–9 Aurora Power score, updated every minute from satellite data.
Open the live tracker →