Recognizing Common Aurora Structures
When you watch the aurora, you’re not just seeing lights — you’re witnessing Earth’s upper atmosphere responding to charged particles in beautiful and complex ways. These displays form distinct **structures**, each with its own behavior, altitude, and meaning. Learning to recognize them not only enhances your viewing experience, but also helps you interpret what kind of geomagnetic activity is occurring in real time.
Below are the most common aurora structures visible to the naked eye or camera, from subtle arcs to explosive coronas.
Aurora Arcs
Arcs are the foundation of most auroral displays. These are horizontal bands of light, usually green, that stretch across the sky from east to west. Arcs often appear early in the night or during quiet geomagnetic conditions.
They’re typically seen low on the northern horizon and can persist for hours before developing into more active forms. Sometimes, arcs brighten and ripple — a sign that a substorm may be approaching.
▲ A low, stable arc hugging the northern horizon before substorm onset
Diffuse Glow
This structure appears as a widespread green haze across the sky, especially after strong substorms. Unlike arcs or rays, it lacks defined structure but may cover large portions of the sky at once.
Diffuse glows can last for hours and may appear in still photos even when faint to the naked eye. They often linger into the early morning hours, marking the last echoes of geomagnetic activity from earlier in the night.
▲ Widespread band of faint green glow across the night sky
Pillars (Rays / Columns)
Rays are vertical beams or columns of auroral light that shoot upward into the sky, often within a larger arc. They occur when electrons penetrate deeper into the atmosphere and excite gases at different altitudes, creating column-like structures.
Rays often appear aligned like piano strings or fence posts, and they’re best seen when the aurora is overhead or during the expansion phase of a substorm. Purple, red, and even blue hues can appear at the tops of rays depending on altitude and atmospheric composition.
▲ Vertical pillars/rays/columns extending above an active arc — often a sign of strong energy input
Curtains
Aurora curtains (also called drapes or bands) resemble shimmering fabric in the sky. They’re formed by overlapping arcs and rays, swaying and fluttering due to variations in the Earth’s magnetic field and incoming particle streams.
These are some of the most dramatic forms for long-exposure photography, often filling the entire sky with layered motion and light. The edges of curtains may ripple or wave — a good indicator of an ongoing substorm expansion.
▲ Curtains with strong motion indicate an active magnetosphere
Pulsating
These are slower, more subtle forms — blotchy areas of light that brighten and fade rhythmically, typically during the recovery phase of a substorm or after prolonged activity. They don’t move across the sky like curtains do, but instead "breathe" in place.
Pulsating auroras tend to be fainter, appear higher in the sky, and can continue for hours. They’re caused by energetic electrons guided into Earth’s atmosphere through fluctuating wave-particle interactions in the magnetosphere.
▲ Subtle, rhythmic patches that pulse rather than swirl
🔭 Coronas
Coronas are rare and breathtaking. This structure forms when an aurora is directly overhead and rays converge at a single point, radiating outward like the spokes of a wheel. It creates the illusion that light is pouring down from the stars above.
To see a corona, you need to be almost directly beneath an active magnetic poleward arc — so they’re often a sign of strong overhead activity. They’re more visible with wide-angle lenses or when lying on the ground looking straight up.
▲ A rare overhead corona — intense, immersive, and fast-moving
What Do These Structures Tell Us?
Each aurora form gives clues about what’s happening above Earth. Faint arcs suggest stored energy. Curtains and rays mean that energy is being released. Pulsating patches often mark the tail end of a storm. Recognizing these structures helps chasers better understand the timeline of auroral events — and when to stay, set up, or start filming.
Over time, you’ll begin to anticipate what’s coming based on what’s already in the sky. Is that arc sharpening? Are rays beginning to split? These signs are nature’s cues — and learning them makes you a better aurora chaser.