Aurora Borealis Colors: What Causes Them and What Colors Can You See?

You may recognize the Northern Lights by their brilliant green glow when in fact the auroral displays are far more diverse in color than most casual observers realize. The palette of the aurora borealis is shaped by atmospheric physics, particle energy, altitude, and the specific gases involved in each reaction. Iceland, due to its geographic location within the auroral oval, is among the best places in the world to observe the full spectrum of auroral phenomena.

Let's explore what colors the aurora can show, what causes the northern lights, and what you can expect in Iceland.

Altitude Matters: Different Colors at Different Heights

Although sources online differ somewhat in the altitude at which each color appears the Canadian Space Agency (CSA) provides good, estimated ranges of where the colors appear in the sky, presented in the table below.

But what happens at these heights?

When charged solar particles enter the Earth's atmosphere and collide with gas molecules — primarily oxygen and nitrogen — those molecules become ionized or excited. As they return to their stable states, they release photons. The wavelength, and therefore color, of those photons depends on the type of gas and its altitude.

Green Northern Lights

Green is by far the most common color observed in Icelandic auroras. It is produced when energetic electrons collide with atomic oxygen (O) at altitudes around 100 to 300 kilometers (60-90 miles) [1]. The specific emission line responsible is at 557.7 nanometers, which falls within the green portion of the visible spectrum. The reason green is so dominant is due to the relative abundance of atomic oxygen at those altitudes and the fact that this energy transition is particularly efficient. The human eye is also more sensitive to green light in dark conditions, which amplifies its visibility even further.

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Red Aurora Borealis

Red auroras are much rarer and occur at significantly higher altitudes, typically above 300 kilometers. These are also caused by atomic oxygen, but through a different energy transition, emitting light at 630.0 nanometers [2] — in the red part of the spectrum. The higher altitude means the density of atmospheric particles is lower, allowing excited oxygen atoms to hold onto their energy longer before releasing it as red light. Because this transition is much slower (on the order of seconds rather than milliseconds), red auroras are easily quenched by collisions in denser parts of the atmosphere and thus require extremely quiet atmospheric conditions to be visible.

Pink Auroras

In strong geomagnetic storms, pink hues may appear near the lower edges of green auroras. These are produced by a mixture of red emissions from atomic oxygen and blue or purple emissions from nitrogen molecules. The combined effect of these emissions in the lower atmosphere — below 100 kilometers — results in pink or magenta tones, often seen as fringes or outlines beneath brighter green arcs. These lower-altitude colors only occur when high-energy particles penetrate deep into the atmosphere, typically during periods of intense solar activity.

Blue and Purple Aurora Colors

Blue and violet auroras are produced primarily by molecular nitrogen (N₂) and ionized molecular nitrogen (N₂⁺) [3]. These emissions happen at altitudes ranging below 100 kilometers, and they involve much higher energy collisions than those that generate green or red light. The emission lines fall around 427.8 nanometers, in the blue and violet range of the spectrum. These colors are much more difficult to observe with the naked eye because human vision in low light is less sensitive to shorter wavelengths like blue and violet. However, they often show up vividly in long-exposure photographs and video, which use sensors more sensitive to this part of the spectrum.

Your 5-Day Northern Lights Hunt Awaits!

White Northern Lights

White or grayish-white auroras can occur when the light is too faint for the eye to resolve into distinct colors, or when multiple colors overlap in a display that is visually saturated [4]. Because the human retina relies more on rod cells (which are not color sensitive) than cone cells in dark conditions, faint auroras often appear as whitish or grey smudges in the sky. Once captured on camera, however, these “white” auroras frequently reveal themselves to contain subtle color variations.

The science behind the colors

The relative intensity and visibility of these colors are influenced by solar activity, altitude, viewing conditions, and even human vision. During intense geomagnetic storms, when particle energy is high and atmospheric penetration is deeper, it's more likely to observe rare colors such as red, pink, and blue. Conversely, during quiet solar periods, green remains dominant due to its lower energy requirement and favorable atmospheric conditions.

Researchers have thoroughly mapped the physical mechanisms behind these emissions using ground-based observations, satellite data, and laboratory spectroscopy. For instance, the University of Alaska Fairbanks Geophysical Institute provides continuous monitoring and modeling of auroral processes. Their data confirms that different auroral forms and their respective altitudes correlate strongly with these color variations. Also, by looking closely at the colors in the aurora, scientists can tell what kind of particles hit the atmosphere and what the atmosphere was made of at that moment. Which they can use to determine space weather impacts and clues about what’s happening in Earth’s upper atmosphere.

Is there an Aurora Color Forecast?

In short, no there's not a specific forecast for aurora colors. To estimate what colors to expect you'd need to combine a few varying factors for example the Kp Index to estimate aurora activity, and a solar activity forecast as blue and pink light may appear during high solar activity, red during intense solar activity, whereas green lights are more energy efficient.

However, the Icelandic Met Office has an aurora forecast on a nine-point scale (Kp index), with 9 signifying an extreme geomagnetic storm and high aurora activity. A Kp 9 event is very rare, happening only every 1-3 years and the most commonly seen events measure around 3.

The rule of thumb of the Kp Index is that the higher the number the more aurora activity, but this doesn't always hold true because more factors in than simply geomagnetic storms. In fact, I remember the brightest northern lights I've ever seen were during a forecast of 3, suggesting "moderate" activity (and those lights were far from moderate). So, just like any forecast that tells you it's a sunny day but your wet jacket tells you otherwise, aurora forecasts are not 100% accurate and should be taken with a... dash of salt.

In Iceland, due to its high-latitude position beneath the auroral oval, observers can often witness green auroras on even moderately active nights during the aurora months. However, if you are hoping to catch more elusive colors like red or blue, the best chances are during geomagnetic storms (Kp index of 6 or above), in areas with minimal light pollution, and on nights when the sky is exceptionally clear.

See the Auroras with Travel Reykjavík

At Travel Reykjavík, we’re here to help you see the magical aurora lights.

With over 80 years of family-run experience (we’ve been welcoming travelers since 1945!), we know just how to turn a northern lights hunt into magic. Choose from our hand-picked selection of small group tours, private tours, multi-day winter escapes, or highland super jeep adventures that take you into the wild.

No matter how you choose to chase the aurora, our goal stays the same: to help you experience the northern lights in their full glory.

Your 5-Day Northern Lights Hunt Awaits!

Sources

1. Canadian Space Agency. (n.d.). The colours of the northern lights. Retrieved from https://www.asc-csa.gc.ca/eng/astronomy/northern-lights/colours-of-northern-lights.asp

2. Royal Belgian Institute for Space Aeronomy. (n.d.). Multi-wavelength observations and modelling of aurora. Retrieved from https://www.aeronomie.be/en/annual-report/multi-wavelength-observations-and-modelling-aurora

3. ChemistryViews. (n.d.). The chemistry behind the aurora borealis (or northern lights). Retrieved from https://www.chemistryviews.org/the-chemistry-behind-the-aurora-borealis-or-northern-lights/

4. NOAA Space Weather Prediction Center. (n.d.). Aurora tutorial. Retrieved from https://www.swpc.noaa.gov/content/aurora-tutorial

5. Howell, E. (n.d.). Aurora colors explained: What causes northern lights to be green, red or purple? Space.com. Retrieved from https://www.space.com/aurora-colors-explained

6. Geophysical Institute, University of Alaska Fairbanks. (n.d.). Aurora forecast. Retrieved from https://www.gi.alaska.edu/monitors/aurora-forecast