Are the Northern Lights Always Green? The Science of Aurora Colors

When most people imagine the Northern Lights, they picture waves of green light rippling across the sky. And it’s true—green is by far the most common aurora color. But the aurora borealis is capable of producing a full palette of colors: red, purple, blue, even pink and white.

The color of the aurora depends on what part of the atmosphere the charged particles collide with and which gases are involved. Let’s break down the science behind this spectacular natural light show.

Why Auroras Happen in the First Place

The Northern Lights are created when charged particles from the Sun (electrons and protons carried by the solar wind) smash into atoms and molecules high above Earth. These collisions excite the atmospheric gases, pushing their electrons into higher energy states.

When those electrons fall back down, they release energy in the form of light. Different gases and altitudes produce different colors.

Think of it like a giant neon sign in the sky—oxygen, nitrogen, and hydrogen each glow in their own unique shades.

The Aurora’s Palette at a Glance

Color	Main Cause	Altitude Range	Notes
Green	Atomic oxygen	100–150 km	Most common aurora color
Red	Atomic oxygen	200–300+ km	Rare, appears as crimson glow
Blue	Molecular nitrogen	Below 100 km	Seen in strong storms
Purple	Nitrogen + oxygen	~100 km	Often fringes of green curtains
Pink	Nitrogen + oxygen	~100 km	Bottom edges, mixes of green and blue
White	Human eye perception	Any altitude	Appears under weak displays

The Most Common Color: Green

• Cause: Oxygen atoms

• Altitude: About 100–150 km above Earth

• Why: At this height, excited oxygen atoms emit light at a wavelength of 557.7 nanometers, which appears as bright green to the human eye.

This is why most aurora photos and reports feature green curtains, arcs, or swirls. Our eyes are also more sensitive to green in low light, which reinforces its dominance.

Red Auroras: Rare and Mysterious

• Cause: Oxygen atoms (again, but higher up)

• Altitude: Above 200–250 km

• Why: At extreme altitudes, oxygen releases a different color—deep red, at 630.0 nanometers.

Red auroras are rarer because they require very high-energy particles and very clear, dark skies. They are often faint, appearing as a soft crimson glow above the more common green bands.

Fun fact: Before the science was understood, many cultures associated red auroras with omens of war or bloodshed.

Purple and Pink Auroras: The Mixers

• Cause: A combination of nitrogen molecules and oxygen

• Altitude: Around 100 km and below

• Why: Excited nitrogen molecules can emit bluish or purplish light. When this mixes with green oxygen emissions, the result is shimmering pink or purple edges at the bottom of auroral curtains.

These colors are especially striking in photographs, though they can sometimes be seen clearly with the naked eye during strong storms.

Blue Auroras: The Rare Glows

• Cause: Molecular nitrogen

• Altitude: Below 100 km

• Why: High-energy electrons colliding with nitrogen molecules create blue or violet light.

Blue auroras are quite rare and usually appear during intense geomagnetic storms. To the naked eye, they often look like deep indigo or violet shadows under the green bands.

White and Multicolored Auroras

Sometimes auroras appear white or grayish to human eyes. This isn’t because they lack color, but because our eyes’ night vision (rod cells) are less sensitive to color in low light. A camera, however, will capture the greens, reds, and purples much more vividly.

During strong solar storms, the aurora can display multiple colors at once—green at mid-levels, red above, purple fringes below—making the whole sky look like a painter’s palette in motion.

“I saw the aurora, but it wasn’t as colorful as in the pictures!”

Why Auroras Look Different to the Human Eye

If you’ve ever stood under the Northern Lights, you may have noticed that the colors sometimes appear white, grayish, or faintly green—but later, your camera shows brilliant reds, purples, and deep blues you didn’t remember seeing.

This difference comes down to the structure of the human eye and how it adapts to light and darkness.

The Two Light Sensors in Our Eyes

The human retina has two main types of light-sensitive cells:

1. Rods

   • Extremely sensitive to low light (night vision).

   • Detect brightness and motion, but not color.

   • About 120 million rods are spread across the retina, especially in the periphery.

   • They give us the ability to see shapes and faint light at night—but in black-and-white.

2. Cones

   • Work best in bright light (day vision).

   • Detect color in three ranges:

     • S-cones (blue)

     • M-cones (green)

     • L-cones (red)

   • About 6 million cones are concentrated in the center of the retina (fovea), giving sharp color vision.

Why Auroras Look Faint to Us

• At night, our eyes switch to “scotopic vision”, dominated by rods. Rods are very sensitive, but they can’t detect color.

• Only when an aurora is bright enough to stimulate cones do we see distinct greens, reds, or purples.

• This is why a faint aurora may look grayish-white to the naked eye, while a strong aurora glows green, and the most powerful storms reveal pinks and reds.

Why Cameras Capture More Color

A digital camera on a tripod can keep its shutter open for seconds, collecting light over time. This builds up faint signals—especially reds and blues—that our eyes cannot register in real-time.

In other words, the camera is “cheating” our biology by integrating more photons than our eyes can process at once.

Dark Adaptation: Letting Your Eyes Adjust

Our eyes need about 20–30 minutes in darkness to fully adapt. During this time:

• The chemical rhodopsin in rods builds up, increasing sensitivity to faint light.

• Cones still function but contribute less to vision.

This means that if you’ve just stepped outside from a brightly lit cabin, the aurora will look much weaker until your eyes adapt.

Fun Twist: Peripheral Vision Sees Auroras Better

Since rods dominate the edges of our vision, faint auroras sometimes appear brighter if you look slightly to the sideinstead of straight at them. Experienced aurora watchers often use this trick to catch dim displays.

So, are the Northern Lights always green? No—green just happens to be the color we see most often. The aurora is really a multi-colored phenomenon, shaped by the chemistry of Earth’s atmosphere and the energy streaming from the Sun.

The next time you look up at an aurora, remember: you’re watching a cosmic light show where oxygen paints in greens and reds, nitrogen adds blues and purples, and your eyes and camera reveal different parts of the spectrum.