Aurora Colors Explained: What They Mean and Why They Happen
Learn why northern lights appear in different colors—green, red, blue, purple, and pink—and what these colors reveal about aurora activity.
Aurora Colors Explained: What They Mean and Why They Happen
Green. Red. Purple. Pink. The northern lights paint the sky in colors that seem almost impossible—colors that vary not just between displays, but within a single night of viewing.
Understanding aurora colors isn't just scientifically interesting; it's practically useful. Colors reveal information about storm intensity, altitude, and what to expect next. This guide explains the science simply and shows you what different colors mean for your aurora experience.
The Science in 30 Seconds
Aurora colors come from atmospheric gases glowing when hit by solar particles. Different gases produce different colors. The altitude where collisions occur also affects the color because atmospheric composition varies with height.
Think of it like neon signs: different gases glow different colors when energized. The sky is a massive "neon display" powered by solar energy.
The Aurora Color Palette
Green: The Most Common Aurora Color
What produces it: Oxygen atoms at 100-300 km altitude
Why it's most common: This altitude range has the optimal combination of:
- High enough oxygen concentration
- Low enough density for atoms to emit light before colliding again
- Sufficient incoming particle energy
| Green Aurora Characteristics | Details |
|---|---|
| Altitude | 100-300 km (60-180 miles) |
| Atom responsible | Atomic oxygen (O) |
| Wavelength | 557.7 nm |
| Typical Kp level | Visible at Kp 1+ at high latitudes |
| Camera sensitivity | Highly visible to both eyes and cameras |
What green aurora tells you: Basic geomagnetic activity is occurring. Green is the "baseline" aurora color—if you see any aurora, you'll likely see green.
Visibility note: Green aurora at 557.7 nm falls within the range where human eyes are relatively sensitive, even in low light. When aurora is too faint for your eyes to see color, cameras will still capture green.
Red: The High-Altitude Glow
What produces it: Oxygen atoms at altitudes above 300 km
Why it's less common: Red emission requires oxygen atoms to stay excited longer (about 2 minutes!) before releasing light. At lower altitudes, atoms collide with neighbors and lose energy before they can emit red light. Only above 300 km is the atmosphere thin enough for this slow emission process.
| Red Aurora Characteristics | Details |
|---|---|
| Altitude | Above 300 km (180+ miles) |
| Atom responsible | Atomic oxygen (O) |
| Wavelength | 630.0 nm |
| Typical Kp level | More common at Kp 4+ |
| Camera sensitivity | Very visible to cameras; fainter to eyes |
What red aurora tells you: Several possibilities:
- Strong geomagnetic storm: High-energy particles reaching higher altitudes
- Top of tall aurora curtains: The upper reaches of intense displays often glow red
- Stable Arc Red (SAR): Rare red glows at mid-latitudes during recovery phase
Visual appearance: Red aurora often appears as a diffuse glow above green curtains, or as an all-red display during intense storms visible at lower latitudes.
Blue and Purple: The Lower-Altitude Colors
What produces them: Nitrogen molecules at 100-200 km altitude
Why they're special: Blue and purple often appear at the lower edges of aurora curtains. These prompt emissions from molecular nitrogen (N₂) and ionized nitrogen (N₂⁺) create the distinctive purple fringing seen on active displays.
| Blue/Purple Aurora Characteristics | Details |
|---|---|
| Altitude | 100-200 km (60-120 miles) |
| Molecule responsible | Nitrogen (N₂) and ionized nitrogen (N₂⁺) |
| Wavelength | 391-470 nm (various bands) |
| Typical Kp level | Usually Kp 4+ |
| Camera sensitivity | Cameras capture better than eyes |
What blue/purple aurora tells you: Intense activity with high-energy particles. Blue and purple often mark the lower edges of active curtains.
Visual appearance: Purple fringing at the bottom of green curtains. Pure blue aurora is rare; it usually mixes with other colors creating various purple and violet hues.
Pink and Magenta: The Mixture Colors
What produces them: A combination of red oxygen emission and blue nitrogen emission
Why they appear: When high-energy particles reach low altitudes while still exciting oxygen, you get red + blue mixing optically = pink/magenta.
| Pink Aurora Characteristics | Details |
|---|---|
| Altitude | 80-100 km |
| Atoms responsible | Oxygen + Nitrogen combination |
| Typical Kp level | Usually during active displays |
| Camera sensitivity | Vivid to cameras; visible to eyes in strong displays |
What pink aurora tells you: Active, dynamic aurora with particles at various energy levels. Pink often appears during substorms and rapidly moving aurora.
Visual appearance: Bright pink lower edges on curtains, or pink "rayed" structures during very active displays.
Yellow and Orange: The Rare Colors
What produces them: Yellow typically results from green + red mixing; orange from red + green in different proportions
Why they're rare: These colors require specific conditions where both oxygen emission altitudes are simultaneously active and visually overlapping.
What they tell you: Complex, multi-altitude aurora activity. Usually occurs during strong storms with deep atmospheric penetration.
Color by Storm Intensity
Aurora colors correlate with geomagnetic activity, though not perfectly:
| Kp Level | Common Colors | What You Might See |
|---|---|---|
| Kp 1-2 | Green only | Faint green arcs on the northern horizon |
| Kp 3-4 | Green, touches of red | Green curtains with red tops during peaks |
| Kp 5-6 | Green, red, purple | Full color spectrum, dancing curtains |
| Kp 7+ | All colors including pink | Overhead aurora with rapid color changes |
Important caveat: These are generalizations. Location, time of night, and specific storm characteristics all affect what colors appear.
Why Your Eyes See Differently Than Cameras
A common frustration: your camera shows vivid purples and reds, but your eyes see mostly white or pale green. This isn't your camera lying—it's physics.
Human Eye Limitations
| Factor | Impact on Aurora Viewing |
|---|---|
| Rod cells | Dominate in low light; poor at color detection |
| Cone cells | Detect color but need more light to activate |
| Green sensitivity | Eyes are most sensitive to green wavelengths |
| Red sensitivity | Poor at detecting faint red light |
Result: During faint aurora, your rod cells see luminosity but not color. Only during bright displays do cone cells activate enough to perceive reds and purples.
Camera Advantages
| Factor | Why Cameras See More |
|---|---|
| Long exposures | Collect light over 5-30 seconds |
| Sensor sensitivity | Modern sensors detect fainter light than eyes |
| Equal color response | Sensors don't favor green like eyes do |
| ISO amplification | Can boost faint signals |
Practical tip: If aurora looks white or faint green to your eyes, take a 10-second photo. The camera will reveal what colors are actually present.
Reading Aurora Colors in Real-Time
Understanding colors helps you interpret what's happening during a display:
Signs of Increasing Activity
| Observation | What It Means |
|---|---|
| Green brightening | Particle flux increasing |
| Red appearing above green | Storm intensifying |
| Purple/pink at bottom edges | High-energy particles arriving |
| Colors becoming more vivid | Substorm may be starting |
| Faster movement | Energy release accelerating |
Signs of Decreasing Activity
| Observation | What It Means |
|---|---|
| Colors fading to pale green | Activity subsiding |
| Red disappearing first | Highest-altitude activity ending |
| Movement slowing | Energy input decreasing |
| Aurora retreating northward | Storm recovery beginning |
Color and Photography
Different aurora colors require different photography approaches:
| Color | Camera Settings Tip |
|---|---|
| Green | Standard settings (ISO 1600-3200, 5-15 sec) |
| Red | Longer exposures help capture faint red |
| Blue/Purple | May appear oversaturated; reduce exposure if needed |
| Pink | Active aurora; use shorter exposures to freeze motion |
| Mixed | Use shorter exposures to prevent color blurring |
White balance note: "Daylight" or "5500K" settings typically produce accurate aurora colors. Auto white balance may shift colors incorrectly.
Regional Color Differences
Your latitude affects which colors you're likely to see:
High Latitudes (65-70°N)
- See aurora more frequently
- Often view the auroral oval from underneath or slightly south
- See more green, with reds and purples during storms
- Aurora can appear overhead
Mid-Latitudes (50-60°N)
- Only see aurora during strong storms (Kp 5+)
- Often view the auroral oval from the south
- Red aurora is relatively more common (viewing through more atmosphere)
- Aurora typically stays on the northern horizon
Lower Latitudes (below 50°N)
- Rare aurora events only (Kp 7+)
- Mostly see red glows on the northern horizon
- "Stable Auroral Red" arcs possible during extreme storms
- Green rarely visible (too far from the auroral oval)
Myths vs. Reality
Myth: "Red aurora means danger"
Reality: Red aurora is scientifically fascinating but poses no danger. The particles creating it never reach ground level.
Myth: "You need Kp 7+ to see colors"
Reality: Green is visible at Kp 1+ from high latitudes. Red and purple become more common at higher Kp, but aren't exclusive to extreme storms.
Myth: "If it looks white, there's no real aurora"
Reality: White aurora is real aurora—your eyes just aren't detecting the colors. Cameras will reveal green and possibly other colors.
Myth: "Aurora colors depend on temperature"
Reality: Colors depend on atmospheric composition and particle energy, not temperature. The -40°C air has the same composition as -10°C air.
Conclusion
Aurora colors are nature's real-time data display. Green tells you "something's happening." Red says "it's intensifying." Purple and pink announce "this is getting exciting." Learning to read these signals enhances both your understanding and your viewing experience.
Next time you're under the aurora, take a moment to study the colors. Note where red appears relative to green. Watch for purple edges. See if you can predict when the next burst of activity might occur based on color changes.
Aurora Go displays color-related data including Bz orientation, Kp index, and real-time activity levels—helping you anticipate what colors might appear tonight.
References
- NOAA Space Weather Prediction Center. "Aurora Tutorial." Emission wavelengths (557.7 nm, 630.0 nm) and altitude ranges.
- NOAA Space Weather Prediction Center. "Tips for Viewing the Aurora." Practical viewing guidance.
- Lancaster University AuroraWatch UK. "The Vivid Lights: What Causes the Colour of Aurora?" Nitrogen emissions and color science.
- NASA Earth Observatory. "Aurora." Camera vs eye sensitivity.