What Causes the Northern Lights? From Solar Storms to Glowing Atoms

The northern lights can look like green curtains, red clouds, or purple fringes dancing across the sky. But behind that shifting spectacle is a chain of events connecting the Sun, Earth’s magnetic field, and individual atoms high above your head.

The basic idea is simple: energetic charged particles collide with atmospheric gases, give them energy, and make them glow. The interesting part is how those particles get there—and why the glow changes color, reaches places such as Spain and Mexico, and often looks brighter on your phone than it does to your eyes.

The Basic Recipe: Particles, Magnetic Fields, and Air

The aurora borealis, or northern lights, occurs when energetic particles—especially electrons, the negatively charged particles found in atoms—enter Earth’s upper atmosphere. The equivalent display in the Southern Hemisphere is the aurora australis.

When an incoming particle hits an oxygen atom or nitrogen molecule, it can transfer some of its energy. The atom or molecule becomes excited, meaning it temporarily holds more energy than usual.

As it returns to a lower-energy state, it can release that energy as a photon: a packet of light.

An aurora is the atmosphere releasing energy as light after being struck by energetic particles.

Different gases, and different changes in their energy states, produce different colors. But before looking closely at those colors, you need to follow the energy from the Sun to Earth.

How the Sun Powers the Display

The Sun constantly releases the solar wind, a stream of charged particles carrying a magnetic field through space.

Earth sits inside a magnetosphere: the region where its magnetic field strongly influences the motion of charged particles. The solar wind compresses this region on the Sun-facing side and stretches it into a long tail on the nightside.

Earth’s magnetic field is a guide, not a giant funnel

It is tempting to imagine the magnetic field simply funneling the solar wind straight into the poles. That picture needs a correction: most of the solar wind flows around the magnetosphere, rather than pouring directly into the atmosphere.

Charged particles within the magnetosphere tend to spiral around magnetic field lines—imaginary lines that show the direction of the magnetic field—and travel along them. Near Earth, the lines connected to auroral regions reach the upper atmosphere at high latitudes. Particles moving down those lines therefore arrive mainly near the poles.

Some solar-wind particles can also enter through the polar cusps, regions on the dayside where the magnetic-field geometry permits relatively direct access.

This helps explain why auroras are concentrated in polar regions. But the magnetic field does more than direct traffic: it also helps store and release the energy that powers the lights.

The magnetotail: an energy reservoir

The stretched nightside part of the magnetosphere is called the magnetotail. Think of it less as a pipe carrying particles to Earth and more as a reservoir of magnetic energy.

A process called magnetic reconnection allows magnetic fields to change how they connect, transferring and releasing energy. The broad sequence is:

1. The solar wind’s magnetic field reconnects with Earth’s field on the dayside.
2. Solar-wind flow carries the connected field lines toward the nightside, adding energy to the stretched magnetotail.
3. Reconnection in the tail releases stored energy and drives particles and energy back toward Earth.
4. Some electrons are accelerated along field lines into the upper atmosphere, producing bright auroras.

The Sun supplies much of the energy, but the particles that ultimately light up the atmosphere need not be the same particles that originally arrived in the solar wind.

As NASA’s aurora overview explains, the display is part of a larger interaction between the solar wind and Earth’s magnetic environment.

Why Auroras Have Different Colors

The color depends mainly on which gas emits the light, which energy transition occurs, and the conditions at that altitude.

An ion is an atom or molecule that has gained or lost electrons and therefore has an electrical charge.

Why the same oxygen can glow green or red

Green and red auroral light can come from the same kind of atom: atomic oxygen, meaning individual oxygen atoms rather than the two-atom oxygen molecules common in the air you breathe.

An atom’s electrons can occupy different energy states. You can picture these as steps on a staircase: an incoming particle supplies energy that raises the atom to a higher step. When it drops to a lower one, the energy difference can emerge as light.

Two important oxygen emissions are:

• Green light, with a wavelength of about 558 nanometers.
• Red light, with a wavelength of about 630 nanometers.

A wavelength describes the spacing of a light wave and determines its color; a nanometer is one-billionth of a meter.

These colors correspond to different transitions between oxygen’s energy states. An oxygen atom that emits green light can even be left in a state capable of emitting red light afterward.

So why does altitude matter? Because each excited state needs time to emit.

Collisional quenching: when an atom loses its chance to glow

The green-emitting state typically lasts about a second before releasing light. The red-emitting state can last roughly two minutes.

Lower in the atmosphere, the air is denser, so collisions are more frequent. Before an oxygen atom has time to emit red light, another collision may remove its energy without producing that red photon. This is called collisional quenching.

Higher up, the air is thinner. With fewer collisions, the atom has a better chance to remain excited long enough to emit red light.

Altitude does not turn oxygen into a different substance. It changes whether an excited atom gets enough uninterrupted time to glow.

This is why oxygen’s red emission tends to survive high in the atmosphere, while green is prominent lower down.

Why blue and purple are less often obvious

Nitrogen is present in ordinary auroras, but its blue and purple emissions are often less prominent to your eyes than oxygen’s green glow.

Nitrogen emissions can stand out near the lower edge of an aurora, where sufficiently energetic electrons have penetrated deeper into the atmosphere. In a bright display, you may see a purple or pink fringe below a green curtain.

Visibility matters too. Your night-adapted eyes struggle to distinguish faint colors, so a camera may record blue or purple that you barely notice.

“Rarer,” then, often means less often visually prominent, not that nitrogen is missing from most auroras.

Why the Lights Reached Spain and Mexico in 2024

Auroras usually occur within the auroral oval, a roughly ring-shaped region around each magnetic pole. During a strong disturbance, that region can expand toward the equator, and the display can become much brighter.

On May 10–11, 2024, several coronal mass ejections—large clouds of magnetized material expelled by the Sun—reached Earth. They produced an extreme geomagnetic storm, a major disturbance of Earth’s magnetic environment.

The event reached G5, the highest level on NOAA’s five-level geomagnetic-storm scale. Its strength allowed people in unusually southerly locations, including Spain and Mexico, to see or photograph auroras.

Was solar maximum responsible?

Solar maximum is the most active phase of the Sun’s roughly 11-year activity cycle. Around this phase, solar eruptions become more frequent.

It was the backdrop to the 2024 event, not its immediate cause.

• Solar maximum made powerful eruptions more likely.
• The particular eruptions that reached Earth caused the storm.
• The resulting geomagnetic disturbance expanded and brightened the auroral display.

That distinction matters: being near solar maximum does not mean every night will bring a spectacular aurora. The specific solar activity and its interaction with Earth determine what happens. NASA’s account of the May storm traces that chain of events.

Why Spain saw so much red

Collisional quenching explains why red oxygen light survives mainly high in the atmosphere. It does not mean red aurora only happens during enormous storms; red can appear above green during less extreme activity too.

From far south, geometry adds another effect. A distant aurora’s high red glow can remain above your horizon while its lower green portion is hidden below it. It is similar to seeing the top of a distant mountain when its base is out of view.

During the May 2024 storm, observers at Spain’s Calar Alto Observatory reported a predominantly red glow toward the northern horizon.

The storm also produced unusually strong red emission at low latitudes. Researchers link some of that emission to processes similar to those behind stable auroral red arcs—red atmospheric glows associated with storm-time heating.

So two factors helped: high-altitude red light was easier to see from far away, and the storm made red emission unusually strong.

Why Your Phone Sees More Color Than You Do

If you see a pale glow but your phone records vivid pink or green, that does not necessarily mean the camera invented the color.

Your eyes use two main types of light-sensitive cells:

• Rods detect faint light well but do not distinguish color.
• Cones detect color but need more light to work effectively.

Under a dark sky, rods do much of the work. A faint aurora can therefore look grayish or whitish even though it is emitting colored light.

A phone in night mode can collect light over several seconds, gathering more signal than you perceive in a brief glance. It may also combine exposures, brighten the result, and process the colors.

The photo is not an exact record of your naked-eye experience—but it can reveal genuine faint emissions. A sufficiently bright aurora can still look richly colored without a camera.

Do Other Planets Have Auroras?

Yes. Jupiter and Saturn both have auroras, though their power supplies and atmospheric light differ from Earth’s.

Jupiter: rotation and moons help power the lights

Jupiter has an enormous, rapidly rotating magnetosphere. Its rotation helps drive auroral activity, and its volcanic moon Io supplies material that becomes charged within that magnetic environment.

Electrical interactions with Io and other moons also produce distinct bright auroral “footprints.” The solar wind influences Jupiter’s auroras, but it is only part of the story.

Saturn: solar wind and rotation both matter

Saturn’s auroras respond strongly to the solar wind, making them more Earth-like in that respect. Its rotating magnetosphere also plays a role.

Both planets have hydrogen-rich atmospheres, unlike the oxygen-and-nitrogen atmosphere responsible for Earth’s familiar colors. Their auroras are commonly studied in ultraviolet light, which your eyes cannot see. Published images often assign visible colors to those ultraviolet observations.

A Light Show Connecting the Sun to Individual Atoms

When you watch an aurora, you are seeing the final step in an enormous transfer of energy: from solar activity, through Earth’s magnetic environment, into particles, and finally into atmospheric light.

The magnetic field guides the particles’ descent. The magnetotail helps store and release energy. Oxygen and nitrogen determine much of the color. Atmospheric density decides which excited states have time to shine—and your eyes or camera determine how much of that glow you notice.

What looks like a curtain in the sky is, at its heart, countless tiny releases of light.