The aurora borealis, commonly known as the northern lights, is a natural light display that occurs when energetic particles from space interact with gases in Earth’s upper atmosphere. The result is a shifting spectacle of green, red, purple, and occasionally blue light that can stretch across the night sky in curtains, arcs, and rippling bands.
The northern lights are most closely associated with regions near the Arctic, including Alaska, northern Canada, Iceland, and Scandinavia. Under favorable conditions, however, they can become visible much farther south, especially during periods of heightened solar activity.
Although the display can look otherworldly, its underlying physics is well understood. The aurora is a visible sign of the connection between the Sun, Earth’s magnetic field, and the atmosphere. Understanding how it forms explains not only its colors and movements but also why it appears in particular places and why it sometimes accompanies disturbances in Earth’s space environment.
What causes the aurora borealis?
The aurora begins with the Sun, whose activity constantly influences the space surrounding Earth.
The Sun releases a continuous stream of electrically charged particles, primarily electrons and protons, known as the solar wind. It also produces occasional eruptions that send additional energy and material into space. Two important examples are solar flares, which are sudden releases of energy and radiation, and coronal mass ejections, which are large expulsions of magnetized plasma from the Sun’s outer atmosphere.
Plasma is a state of matter made up of charged particles. When solar plasma and its embedded magnetic field interact with Earth’s magnetic environment, they can transfer energy into the region surrounding our planet.
Earth’s magnetic field, generated mainly by the movement of electrically conducting material in its outer core, creates a protective magnetic environment called the magnetosphere. This region deflects much of the solar wind around Earth, but it does not block every interaction. Energy and particles can enter the magnetosphere through several processes, including the interaction of the solar wind’s magnetic field with Earth’s magnetic field.
Some of this energy is stored in the magnetosphere and later released into Earth’s upper atmosphere. Electrical processes in near-Earth space accelerate electrons toward the atmosphere, particularly along magnetic field lines that connect the magnetosphere to the polar regions.
When these electrons descend into the upper atmosphere, they collide with atoms and molecules of oxygen and nitrogen. The collisions transfer energy to those atmospheric particles. As the excited particles return to lower-energy states, they release some of that energy as light.
That light is the aurora.
The entire process links solar activity to Earth’s magnetic field and atmospheric chemistry. The colors that people see are the final result of energy moving through this interconnected system.
Why the northern lights have different colors
Auroras can appear green, red, purple, pink, or blue. Their colors depend mainly on which atmospheric gas emits the light, the energy delivered by incoming particles, and the altitude at which the collisions occur.
Earth’s upper atmosphere contains mostly nitrogen and oxygen, but these gases do not emit light in exactly the same way. Each has its own set of energy levels, so each produces characteristic wavelengths when excited particles release energy.
Green: the most familiar auroral color
Green is the color most commonly associated with the northern lights. It is produced primarily by oxygen atoms at altitudes of roughly 100 to 150 kilometers, or about 60 to 90 miles, above Earth’s surface.
When an oxygen atom absorbs energy from a collision, it can enter an excited state. As it returns to a lower-energy state, it emits green light. The particular transition responsible for the familiar green aurora occurs at a wavelength near 557.7 nanometers, within the visible spectrum.
This emission is especially prominent because the relevant excited state can radiate efficiently under the conditions found at these altitudes.
Red: oxygen at higher altitudes
Oxygen can also produce red auroral light, usually at greater altitudes than the familiar green emission. A prominent red emission occurs near 630 nanometers.
This red light is associated with an excited state that takes longer to release its energy. At lower altitudes, collisions with other atmospheric particles can interrupt the process before the oxygen atom emits the red photon. Higher in the atmosphere, where the gas is thinner and collisions are less frequent, the emission has more opportunity to occur.
Red auroras can therefore extend well above green ones. They may appear as faint crimson glows or broad red structures, sometimes visible above a brighter green display.
Blue, purple, and pink: nitrogen emissions
Nitrogen molecules and nitrogen ions can produce blue and purple light when energized by incoming particles. These emissions often occur at lower altitudes than the main green oxygen emission, although the exact distribution depends on the auroral event.
Pink and magenta colors can appear when nitrogen emissions overlap with red or green light. The resulting appearance depends on the relative intensity of the different emissions and on how the human visual system perceives their mixture.
An aurora does not have to display every color. Many events are predominantly green, while others include distinct red or purple regions. Color alone does not provide a complete measure of an aurora’s strength because atmospheric conditions, particle energy, and viewing conditions all influence what becomes visible.
Why the aurora forms rings around Earth’s poles
The northern lights tend to appear in a broad region surrounding the Arctic rather than directly over the geographic North Pole at all times. This region is called the auroral oval.
The oval is centered approximately on Earth’s magnetic pole, which differs from the geographic pole defined by Earth’s rotation axis. Earth’s magnetic field guides many charged particles along magnetic field lines, and the auroral oval marks a region where particle precipitation into the atmosphere is especially common.
The oval is not a fixed circle. Its position, width, brightness, and shape change as solar wind conditions and Earth’s magnetosphere change.
During relatively quiet periods, the most active auroral displays are generally concentrated at high latitudes. When the solar wind transfers more energy into the magnetosphere, the oval can expand toward lower latitudes. This is why a strong geomagnetic storm can make the northern lights visible in parts of the United States that rarely see them under ordinary conditions.
A similar process occurs in the Southern Hemisphere. There, the corresponding phenomenon is called the aurora australis, or southern lights. Both displays arise from the same fundamental interaction between solar particles, Earth’s magnetic field, and the upper atmosphere.
The northern and southern auroras are related, but they do not always form identical patterns at the same time. Differences in magnetic field geometry, atmospheric conditions, and solar wind interactions can affect their appearance.
Why the northern lights move and change shape
Auroras are dynamic because the processes that produce them are constantly changing. Their movement reflects variations in electric fields, magnetic fields, and the flow of energetic particles through Earth’s near-space environment.
A display may begin as a faint arc along the northern horizon. It can then brighten, develop folds and ripples, or spread into several parallel bands. During a more active event, the aurora may expand overhead and break into rapidly changing patches of light.
These structures are associated with the organization of charged particles and electrical currents in Earth’s magnetosphere and upper atmosphere. The currents flow through space and the ionosphere, an electrically conductive region of the upper atmosphere. Their changing patterns influence where particles are accelerated into the atmosphere and where auroral light is produced.
A particularly active phase is known as an auroral substorm. During a substorm, energy stored in the magnetotail—a region of Earth’s magnetosphere stretched away from the Sun—can be released and redistributed. The aurora may brighten rapidly, expand in area, and develop complex moving structures.
Although auroral forms can look like physical curtains waving in the wind, they are not solid sheets of material. They are regions of atmospheric gas emitting light. Their apparent motion comes from changes in where energetic particles enter the atmosphere and where those particles excite atmospheric gases.
The light is produced high above the ground, so the display can extend across a large part of the sky. What looks like a single ribbon may contain many distinct regions of particle precipitation and light emission.
Where and when can you see the northern lights?
The best chances of seeing the aurora borealis are generally in high-latitude regions beneath or near the auroral oval. However, a successful viewing depends on more than location alone.
Where the northern lights are most visible
Alaska and northern Canada are among the best-known viewing destinations in North America. In Alaska, places away from city lights can offer excellent opportunities to see the aurora. In Canada, northern communities and wilderness areas provide similarly favorable conditions.
Across the Atlantic, Iceland, northern Norway, Sweden, and Finland are popular destinations because they lie at auroral latitudes and offer access to dark landscapes. Parts of Greenland and northern Russia also fall within the broad region where auroras frequently occur.
You do not have to travel to the Arctic to see the northern lights, however. During sufficiently strong geomagnetic storms, the auroral oval can expand far enough south to make displays visible across more of the United States. The latitude reached by an individual event varies, so no particular location is guaranteed to see an aurora during a storm.
For any viewing destination, dark skies are important. Artificial light reduces the contrast between the aurora and its surroundings, making faint displays harder to see. Cloud cover can hide the lights entirely, even when geomagnetic conditions are favorable.
The best time of year
Auroras can occur throughout the year because the Sun continually supplies the energy that drives them. In practice, they are easiest to observe during dark nights, making the darker seasons more useful for viewing at high latitudes.
Autumn, winter, and early spring often provide longer periods of darkness in Arctic regions. Winter can offer many hours of nighttime viewing, although temperatures and weather may make outdoor observation challenging.
The equinoxes, which occur around March and September, are often associated with favorable geomagnetic conditions. Researchers have observed seasonal patterns in geomagnetic activity, and the geometry of the solar wind’s magnetic field relative to Earth’s magnetic field helps explain some of these patterns. This does not mean that auroras occur only near the equinoxes or that a display is guaranteed on any particular date.
The time of night matters, too. Auroras can appear at different times, but activity is often concentrated around local magnetic midnight, which does not necessarily coincide exactly with midnight on a clock. The strongest part of a display may last only a short time, or the aurora may remain visible for several hours.
How weather and light pollution affect visibility
Clear skies are essential because the aurora occurs above the clouds but must be viewed through them. Even an intense display can remain invisible beneath a thick cloud layer.
Moonlight and artificial lighting also affect visibility. A bright moon does not prevent an aurora from occurring, but it can make faint structures less noticeable. Moving away from cities, stadiums, parking lots, and other bright sources improves contrast.
A location with a wide view of the northern horizon is useful when auroral activity is weak or concentrated at high latitudes. During stronger displays, the lights may extend overhead or appear in several directions.
How solar activity influences auroras
Auroral activity is closely tied to conditions on the Sun, but predicting a particular display is more complicated than simply checking whether the Sun is active.
The Sun follows an approximately 11-year cycle in the number of sunspots and in several related measures of solar activity. Sunspots are relatively dark regions on the solar surface associated with concentrated magnetic fields. Periods of greater solar activity often include more flares and coronal mass ejections, increasing the opportunities for strong interactions with Earth’s magnetosphere.
However, not every solar flare produces a visible aurora on Earth. A flare releases electromagnetic radiation, which travels at the speed of light and can affect Earth’s upper atmosphere and radio communications. A coronal mass ejection, by contrast, can carry a large amount of magnetized plasma through interplanetary space. If it reaches Earth and its magnetic field is oriented favorably for transferring energy into Earth’s magnetosphere, it can drive a geomagnetic storm.
The orientation of the arriving magnetic field is particularly important. When the interplanetary magnetic field points southward for a sustained period, it can connect more effectively with Earth’s northward-pointing dayside magnetic field through a process called magnetic reconnection. This process allows energy and magnetic flux to enter the magnetosphere, often increasing geomagnetic activity.
A fast solar wind or a large coronal mass ejection does not automatically guarantee a major aurora. The structure, speed, and magnetic orientation of the solar material all influence the outcome.
Scientists monitor solar activity, solar wind conditions, and changes in Earth’s magnetic field to estimate the likelihood of auroras. Forecasts can indicate when conditions are favorable, but the exact timing, location, brightness, and appearance of a display remain difficult to predict with precision.
What is the difference between the aurora borealis and the aurora australis?
The aurora borealis and aurora australis are the northern and southern versions of the same natural phenomenon.
The name aurora borealis comes from terms associated with dawn and the north, while aurora australis refers to the south. Both result from energetic particles entering the upper atmosphere and exciting oxygen and nitrogen.
Their colors, heights, and general forms can be similar because the two hemispheres share the same basic atmospheric physics. Both can display arcs, bands, curtains, and diffuse glows.
Their geographic settings differ. The northern lights are observed most often from Arctic and sub-Arctic regions, while the southern lights are most accessible from Antarctica and some high-latitude locations in the Southern Hemisphere. The southern aurora is often less familiar to the public because much of its most favorable viewing region lies over the Southern Ocean and Antarctica, where relatively few people live.
The two auroras are magnetically connected in some circumstances and can show related patterns. Nevertheless, they are not always mirror images. The orientation of Earth’s magnetic field, differences in local conditions, and variations in the solar wind can produce different structures in each hemisphere.
How high above Earth do the northern lights occur?
Most visible auroral emissions occur in the upper atmosphere, broadly within an altitude range of about 80 to 500 kilometers, or roughly 50 to 310 miles. The exact altitude depends on the type of emission and the energy of the incoming particles.
The familiar green oxygen emission is commonly strongest around 100 to 150 kilometers above Earth’s surface. Some red oxygen emissions occur considerably higher, while certain blue and purple nitrogen emissions can be prominent at lower altitudes.
These heights place the aurora well above ordinary weather systems, which take place in the lower atmosphere. Auroras are not caused by clouds, wind, rain, or other everyday weather processes, although clouds can prevent observers from seeing them.
The altitude also explains why auroras can appear to cover an enormous portion of the sky. A light-producing region hundreds of kilometers above the ground can be visible from great distances, depending on its brightness, the observer’s location, and the curvature of Earth.
Despite their apparent closeness during an intense display, auroras are not occurring just above mountain peaks or in the clouds. They form in a rarefied region of the atmosphere where collisions between energetic particles and atmospheric gases produce light.
Can the northern lights affect people and technology?
The visible aurora itself is not dangerous to people watching from the ground. The particles that produce it deposit their energy high in the atmosphere, and Earth’s atmosphere shields people at the surface from most of their direct effects.
However, the solar and geomagnetic activity that produces strong auroras can affect technological systems. These effects are part of what scientists call space weather: changing conditions in the Sun, solar wind, magnetosphere, and upper atmosphere that can influence human technology.
During a strong geomagnetic storm, changes in Earth’s magnetic field can induce electrical currents in long conductors on the ground. Power transmission networks are especially relevant because geomagnetically induced currents can interfere with transformers and other equipment. The risk depends on storm intensity, local geology, grid design, and the characteristics of the electrical system.
Geomagnetic disturbances can also affect satellites by changing the radiation environment and heating the upper atmosphere. Heating can increase atmospheric density at satellite altitudes, increasing drag on some spacecraft and altering their orbits. Radiation and energetic particles can disrupt satellite electronics or contribute to operational problems.
Radio communication and navigation systems can also be affected. Disturbances in the ionosphere can alter the propagation of radio waves and introduce errors into satellite-based positioning systems. High-frequency radio communications, which are important for some aviation and maritime operations, can be particularly vulnerable to certain kinds of solar disturbance.
These impacts do not occur every time the northern lights appear. Ordinary auroral displays are a normal feature of Earth’s interaction with the solar wind. Significant technological effects are more closely associated with the underlying solar and geomagnetic disturbance, especially during strong space weather events.
Aurora observations are therefore scientifically useful beyond their visual appeal. They help researchers study how energy enters Earth’s magnetosphere, how charged particles move through space, and how disturbances in the solar environment can affect our planet.
How scientists study the aurora
Scientists use a combination of ground-based observations and space-based instruments to understand auroral activity.
Ground-based cameras photograph the changing shapes and colors of the aurora. Specialized optical instruments can measure the wavelengths of emitted light, helping researchers identify the atmospheric species responsible for different emissions and estimate conditions in the upper atmosphere.
Radar systems can investigate the movement and properties of ionized gas in the ionosphere. Magnetometers measure changes in Earth’s magnetic field, allowing researchers to track electrical currents and geomagnetic disturbances associated with auroral activity.
Satellites provide measurements of the solar wind, Earth’s magnetic field, and energetic particles in space. Some spacecraft observe the magnetosphere directly, while others monitor the solar wind upstream of Earth to help estimate how incoming conditions may affect the planet.
By combining these observations, scientists can investigate where auroral particles originate, how they gain energy, and why displays change so rapidly. The basic mechanism of auroral light production is established, but researchers continue to study the details of energy transfer, particle acceleration, and the organization of complex auroral structures.
Why the northern lights matter
The aurora borealis is more than a beautiful night-sky display. It reveals an active relationship between the Sun and Earth that cannot be understood by studying either in isolation.
Its light records the energy delivered by charged particles to the upper atmosphere. Its shape and movement reflect changing conditions in Earth’s magnetic environment. Its connection to geomagnetic storms also offers insight into space weather, which can affect satellites, navigation, radio communication, and electrical infrastructure.
For observers, the northern lights may appear mysterious because they emerge without sound and change shape across a vast, dark sky. For scientists, they are a visible expression of physical processes occurring across enormous distances, from the Sun to Earth’s magnetosphere and down into the thin air high above the ground.
The essential explanation is straightforward: solar activity supplies energy, Earth’s magnetic field helps direct charged particles toward the polar regions, and atmospheric oxygen and nitrogen release light when those particles collide with them. The resulting colors and moving forms make the aurora one of the clearest visible demonstrations of how our planet interacts with the space around it.
