How Do Northern Lights Form?

It All Starts with the Sun

The sun constantly sends a stream of particles into space — this is called the solar wind. The particles, mainly electrons and protons, travel through space at 300–800 km/s. Normally the solar wind is steady and doesn't cause significant aurora on Earth.

But massive particle clouds occasionally erupt from the sun's surface, called Coronal Mass Ejections (CMEs). These eruptions contain billions of tonnes of charged particles and can be many times stronger than normal solar wind. CMEs are the main source of aurora storms.

The sun's surface also features sunspots — dark, magnetically active areas. More sunspots mean more likely CMEs. The sun's 11-year activity cycle determines sunspot numbers — and therefore aurora strength and frequency.

Earth's Magnetic Field — The Invisible Shield

Earth is like a giant magnet. Its magnetic field, called the magnetosphere, extends tens of thousands of kilometres into space and deflects most of the solar wind past Earth. Without this protection, the solar wind would strip away our atmosphere — as has happened to Mars.

But near the poles — exactly where Levi is located — the magnetic field has a different structure. Near the poles, field lines curve towards Earth's surface, creating a "funnel" through which solar wind particles can penetrate the atmosphere.

This area is called the aurora oval — a ring-shaped zone around each polar region, typically at latitudes 65°–75° N. Levi (67.8° N) sits in the heart of this zone, making it one of Europe's best places to see northern lights.

Collisions in the Atmosphere — The Light Show Begins

When solar wind particles (electrons) enter the atmosphere through the magnetic field funnel, they begin colliding with atmospheric gas atoms — mainly oxygen and nitrogen. These collisions occur at 100–300 kilometres altitude above Earth's surface.

In a collision, the gas atom becomes excited — it receives extra energy from the electron. The excited state is unstable and the atom wants to return to normal. When the excited state releases, the atom emits the excess energy as light. This light is the aurora.

Different gases and altitudes produce different colours:
• Green — oxygen at 100–200 km altitude (most common)
• Red — oxygen above 200 km altitude (rarer)
• Purple/blue — nitrogen (often at the lower edge of aurora curtains)

A single aurora display can involve millions of these tiny light reactions simultaneously — the result is a moving, undulating light show across the sky.

Why Near the Poles?

The aurora oval is a ring-shaped zone around polar regions, typically at latitudes 65°–75° north and south. This is the area where aurora occurs most frequently — and Levi (67.8° N) is near the southern edge of the northern oval. An excellent location.

The oval exists because of Earth's magnetic field structure: near the poles, field lines "open up" and allow solar wind particles into the atmosphere. At the equator and temperate latitudes, the magnetic field effectively deflects particles away.

During very strong geomagnetic storms (KP 7+), the aurora oval expands significantly southward. Aurora can then be seen even in Central Europe — Germany, Poland, even northern Italy. In May 2024, such a storm produced aurora visible as far south as Spain. In Levi, these storms are spectacular: the entire sky burns green, red and purple.

Different Forms

Northern lights appear in many forms, and recognising them enriches the viewing experience:

Arc — The most common form. A green or pale green arc on the northern sky, often fairly static. This is typically the first sign of aurora in the evening.

Curtain — A moving, undulating structure resembling a curtain blowing in the wind. Very beautiful and dynamic. Forms when the magnetic field is active and particle flows change rapidly.

Corona — A radial structure directly overhead. Visible when you're directly beneath an aurora curtain looking up. Impressive and rare experience.

Patches and glow — Faint, diffuse light areas in the sky. Often the "early stage" of aurora before a stronger display.

The form depends on the local structure of the magnetic field and particle energy. The same evening can show several different forms as aurora intensity changes.

How High Are They?

Northern lights typically occur at 100–300 kilometres altitude in the atmosphere. This is the so-called thermosphere — an extremely thin atmospheric layer where gas is so sparse that normally no visible phenomena occur.

Green aurora occurs at approximately 100–200 km altitude — at this height, oxygen atoms react quickly and release energy as green light.

Red aurora occurs higher, at 200–300 km. At this altitude, oxygen atoms excite differently and the reaction is slower, producing red light.

For comparison: aircraft fly at about 10 km altitude. The International Space Station (ISS) orbits at 400 km — so aurora is below the ISS! Astronauts often photograph aurora from above, offering a unique perspective.

Aurora's altitude explains why it's visible over such a wide area: the aurora you see in Levi may physically be located 500–1000 km to the north, but because it's so high, it's visible low on the horizon even from far away.

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