What Causes the Northern Lights?
The northern lights start on the Sun and end about 60 to 200 miles above your head. Here is the chain of events, step by step, without the jargon.
Short answer: The northern lights are caused by charged particles from the Sun that reach Earth's magnetic field and are steered down into the upper atmosphere near the poles. There they collide with oxygen and nitrogen, which release the energy as light. The color depends on which gas is hit and at what altitude.
It starts with the solar wind
The Sun sends out a constant stream of charged particles, mostly electrons and protons. This stream is called the solar wind. It flows past Earth at about 250 miles per second (400 km/s) on a typical day, and faster after solar outbursts.
The Sun also has outbursts. A coronal mass ejection (CME) throws a huge cloud of magnetized gas into space. Fast streams from coronal holes, dark areas in the Sun's outer layer, also raise the solar wind speed. When either one reaches Earth, aurora activity usually goes up.
Earth's magnetic field catches part of it
Earth is wrapped in a magnetic field called the magnetosphere. Most of the solar wind flows around it. The key factor is the direction of the magnetic field carried by the solar wind.
When that field points south (scientists call this a negative Bz), it links up with Earth's field, which points north on the day side. Energy and particles then leak into the magnetosphere and build up in its long tail on the night side. When that stored energy is released, particles race down along the field lines toward the poles.
This is why the solar wind's direction matters as much as its speed. You can see these values on our Kp index page.
Oxygen and nitrogen make the light
The incoming electrons hit atoms and molecules in the upper atmosphere. Each collision pushes the gas into an excited state. When it settles back down, it gives off a small burst of light. Billions of these bursts make the glow you see.
- Oxygen makes the common green light and the deep red light high up.
- Nitrogen makes blue and violet light, plus the pink or magenta edge sometimes seen at the bottom of bright curtains.
The same physics lights a neon sign: an electric current excites a gas, and the gas glows in its own color. Our guide to aurora colors explains each color in detail.
How high the aurora is
Most aurora happens between about 60 and 200 miles (100 to 320 km) up. That is far above clouds, planes and weather, and well below most satellites.
| Height | Main gas | Typical color |
|---|---|---|
| About 150 miles and higher | Oxygen | Red |
| About 60 to 150 miles | Oxygen | Green |
| Below about 60 miles | Nitrogen | Pink, blue, violet |
These heights are rough. They shift with the energy of the incoming particles.
Why it happens near the poles
Earth's magnetic field lines come together near the magnetic poles and dip into the atmosphere there. The particles follow those lines, so they reach the air in two rings around the poles. These rings are called the auroral ovals.
In the north, the oval usually passes over Alaska, northern Canada, Iceland and northern Scandinavia. In the south, it circles Antarctica, and the light is called the aurora australis, or southern lights.
During a strong geomagnetic storm, the ovals grow wider and push toward the equator. That is when people in the northern US, the UK or southern Australia get a chance. See how far south you can see the northern lights for details.
Why the aurora moves and changes
The aurora is not steady because the solar wind is not steady. Small changes in speed, density and field direction shift where particles enter the atmosphere.
A common pattern is the substorm. A quiet arc brightens, then breaks into moving curtains and rays that can fill the sky for 10 to 30 minutes. After that, the display often fades to faint, pulsing patches. Several substorms can happen in one night.
Questions people ask
Are the northern lights dangerous?
The aurora itself happens far above the ground and poses no risk to people watching it. Strong geomagnetic storms can affect power grids, satellites and radio signals, which agencies such as NOAA monitor.
Do the northern and southern lights happen at the same time?
Yes, they usually happen at the same time, because both are driven by the same solar wind. The two displays are often similar in shape, though not identical.
Can you hear the northern lights?
Some people report faint crackling or clapping sounds during strong displays. Researchers have studied the claim, but it is rare and the cause is still debated.
Why is the aurora stronger some years?
The Sun follows an activity cycle of about 11 years. Around the peak there are more sunspots, flares and CMEs, so strong geomagnetic storms happen more often.
Written by the aurorahour team from published science and NOAA data. General information, not a promise of any display. Last checked: October 2026.