What is the 'Series' of Events That Creates the Northern Lights?

When we watch the Northern Lights, we’re seeing the grand finale of a cosmic story—a series of events that connects the Sun directly to our sky. This natural spectacle isn’t a single occurrence but the result of a dynamic process involving immense energy, vast distances, and the fundamental physics of our solar system. Understanding this ‘series’ transforms the viewing experience from simple wonder into a deeper appreciation for the powerful forces at play.

This guide breaks down the entire process, from the initial solar eruption to the final, shimmering curtains of light, explaining each step in this celestial chain reaction.

The entire story of the aurora begins with our star, the Sun. It acts as the engine, constantly sending out the energy and particles that are the essential ingredients for the Northern Lights.

The Source: Solar Activity

The Sun’s surface is a turbulent place. It constantly emits a stream of charged particles, primarily electrons and protons, known as the solar wind. This wind flows outward in all directions. However, the intensity of this wind isn’t constant. The Sun goes through an approximately 11-year cycle of activity, moving from a quiet solar minimum to a very active solar maximum. During active periods, events like solar flares (intense bursts of radiation) and Coronal Mass Ejections (CMEs) (massive clouds of solar plasma) can occur. It is these powerful CMEs that are responsible for the most intense and widespread aurora displays on Earth.

The Journey: The Interplanetary Voyage

Once ejected from the Sun, these particles begin their journey across the 93 million miles (150 million km) to Earth. The regular solar wind travels at speeds around 1 million mph (1.6 million km/h), typically taking 2 to 4 days to reach our planet. However, a fast-moving CME can make the trip in as little as 18 hours. During this voyage, the cloud of particles carries with it a piece of the Sun’s magnetic field, known as the Interplanetary Magnetic Field (IMF). The orientation of this field is a crucial factor in determining whether a strong aurora will occur when it finally reaches Earth.

The Arrival: A Clash with Earth’s Shield

Earth is protected from the constant barrage of solar wind by its magnetosphere, an invisible magnetic shield generated by the planet’s molten core. When the solar wind arrives, the magnetosphere deflects most of it. However, if the arriving IMF is oriented opposite to Earth’s magnetic field (a ‘southward Bz’), the two fields can connect. This process, called magnetic reconnection, opens a gateway, allowing huge amounts of energy and particles to be transferred from the solar wind and funneled down the magnetic field lines toward the polar regions. This is the critical step that powers up the auroral light show.

After the solar particles have been captured and guided by the magnetosphere, the final and most beautiful part of the series begins in Earth’s upper atmosphere.

The Collision: Creating Light from Gas

As the energized particles are funneled towards the poles, they accelerate and plunge into Earth’s upper atmosphere at incredible speeds. Here, between 60 to 200 miles (100-320 km) high, they collide with atoms and molecules of gas, primarily oxygen and nitrogen. These collisions transfer energy to the atmospheric atoms, putting them in an ‘excited’ state. To return to their normal state, the atoms must release this excess energy. They do so by emitting a tiny particle of light, called a photon. When billions of these collisions happen simultaneously, the combined light of all those photons creates the aurora we see.

The ‘Episodes’: Different Aurora Shapes

The aurora is not static; it’s a dynamic, evolving display. The ‘series’ can feature different ‘episodes’ or forms. It often begins as a simple, quiet arc stretching across the sky. As the energy input increases, this arc can develop into moving, shimmering curtains or ‘drapes’ of light that seem to dance. During the most intense periods of a geomagnetic storm, known as a substorm, the aurora can explode across the entire sky, forming a dazzling, overhead corona where the lights appear to radiate from a single point. These changing shapes reflect the complex and shifting interactions between the solar wind and the magnetosphere.

• The aurora is a multi-step ‘series’ of events, not a single phenomenon.
• It begins with the Sun releasing charged particles, either as a steady ‘solar wind’ or a powerful ‘CME’.
• The journey to Earth for these particles typically takes 1-4 days.
• Earth’s magnetic field (magnetosphere) acts as a shield but also funnels particles toward the poles.
• The light is created when solar particles collide with oxygen and nitrogen atoms high in the atmosphere.
• The intensity and form of the aurora, from a simple arc to a dancing curtain, depend on the level of solar activity.
• The most powerful auroras are caused by Coronal Mass Ejections (CMEs) from the Sun.

Q: Does this ‘series’ of events happen every night? A: Yes, the basic process of solar wind interacting with the magnetosphere happens constantly. However, the strength of this interaction varies greatly, so a visible aurora is not guaranteed every night, especially at lower latitudes.

Q: What is a geomagnetic storm? A: A geomagnetic storm is a major disturbance of Earth’s magnetosphere that occurs when a very efficient exchange of energy from the solar wind happens. These storms are often caused by CMEs and result in intense, widespread auroras.

Q: How long does a typical aurora display last? A: An auroral display can be brief, lasting only 10-15 minutes, or it can be a series of events that lasts for several hours. The most active periods, called substorms, typically last for about 30-60 minutes at a time.

• NOAA Space Weather Prediction Center – The Science of the Aurora
• SpaceWeatherLive – What is a Coronal Mass Ejection (CME)?
• University of Alaska Fairbanks – Aurora Science & Information