Auroras, the Sun, and a Firehose of Science: What I Learned at Astronomy Club

At our latest astronomy club meeting, Dr. Robin Metcalfe treated us to a fascinating presentation on the science behind auroras. Dr. Metcalfe directs the Division of Natural Sciences at York University in Canada. Her talk, titled “Astrosleuthing an Aurora,” blended stunning visuals, cultural insight, and a deep dive into the science of these mysterious lights. Below is a summary of the key scientific takeaways from her presentation, with a few club anecdotes thrown in.

What Is an Aurora?

The aurora borealis (“northern dawn”) gets its name from the Roman goddess of dawn (Aurora) and the Greek god of the north wind (Boreas). The aurora australis is its southern counterpart—literally meaning “Southern Dawn,” a mirror to its northern namesake.

Indigenous peoples around the world often interpret auroras as spiritual—many believing them to be ancestral spirits.

Auroras are most common at high latitudes (closer to the poles), but strong solar activity can push them closer to the equator—as we recently witnessed right here in Florida!

I’ll admit—I had to look up how latitude works. Turns out 0° is the equator, and 90° marks the poles—both north and south. So “higher” latitude doesn’t mean farther north—it means farther from the equator, whether you're heading toward the Arctic or Antarctic. And “lower” latitude just means you’re closer to the middle.
That’s why auroras usually stay near the poles—unless the Sun gets rowdy.

But while auroras have inspired wonder for millennia, what they actually are is a story that took centuries to piece together. It begins not on Earth, but with the Sun—its magnetic cycles, its flares, and the storms it hurls through space. Understanding the Sun’s behavior was the first step toward unraveling the mystery of auroras.

The Origins of Auroras: From Myth to Science

One of the earliest suspected records of an aurora comes from 10th century BCE China: “During the night, a five-coloured light penetrated the Northern Sky…”

Fast-forward to modern science:

• 1908: George Ellery Hale discovers sunspots are caused by intense magnetic fields.
• 1942: James Stanley Hey links sunspot activity with radio interference, marking the birth of radio astronomy.

During World War II, British military officials were puzzled by radar interference that seemed to come from space. Physicist James Stanley Hey was tasked with figuring it out, and in 1942, he discovered that the interference was tied to sunspot activity. His work marked the beginning of radio astronomy—and helped reveal that sunspots emit radio waves.

How the Sun Sets the Stage

We now know the Sun’s magnetic field, generated by its rotating plasma layers, twists and tangles over time. These tangled fields erupt from the surface as loops, creating sunspots and releasing charged particles. In fact, by tracking how sunspots move across the Sun’s face, early astronomers discovered that different parts of the Sun rotate at different speeds—faster at the equator than at the poles. This unequal spin, called differential rotation, is a defining feature of the Sun’s dynamic behavior.

Ultraviolet images of the Sun reveal massive magnetic loops rising from its surface, often anchored at sunspots. These loops illuminate the powerful forces involved in solar flares and are key to understanding how the Sun’s magnetic field stores and releases energy.

Interestingly, sunspots appear dark not because they’re actually dark, but because they are cooler than the surrounding surface, making them stand out in contrast.

Earth’s magnetic field, generated by its spinning liquid iron core, behaves like a giant bar magnet tilted slightly off-center. It forms protective magnetic field lines that arc around the planet and converge at the poles. These field lines are what guide charged solar particles toward the polar regions, setting the stage for auroras.

When these particles hit Earth’s magnetic field, they funnel toward the poles. There, they collide with atmospheric atoms—exciting them and causing them to emit light. Voilà: aurora. All those sunspots, flares, and magnetic twists? This is where it all leads. The sky lights up—and now we finally understand why.

Color, Cycles, and Chaos

Auroral colors come from excited gases:

• Green = monatomic oxygen (O) — the most common auroral color
• Red = oxygen (rare, high altitudes)
• Blue = ionized nitrogen (N₂⁺); purple and other hues may include minor contributions from hydrogen and helium

Stronger geomagnetic storms—especially near the peak of the Sun’s 11-year cycle—can trigger a wider range of auroral colors.

This 11-year solar cycle was first discovered in the mid-1800s by Heinrich Schwabe—an amateur astronomer (that’s us!) who noticed patterns in sunspot frequency while observing the Sun over 17 years. His dedication helped lay the groundwork for modern solar science.

We’re currently approaching a solar maximum predicted to peak in 2025—and it’s already more intense than expected, with nearly twice as many solar flares as models predicted!

Strong solar storms can cause:

• Satellite disruptions
• GPS and telecom interference
• Power grid blackouts (like the surprising May 1921 geomagnetic storm, which occurred near a solar minimum and serves as a reminder that there’s still much to learn about the Sun’s behavior and its effects on Earth)

Auroras in the Ancient Record: The 2023 Study

A 2023 study by Bard et al. provided one of the most striking pieces of evidence linking auroras to ancient solar storms (Phil. Trans. R. Soc. A, DOI: 10.1098/rsta.2022.0206). Scientists discovered a sharp spike in carbon-14 levels preserved in tree rings from 14,300 years ago. This spike matched a corresponding beryllium-10 anomaly found in polar ice cores—strong evidence of a massive solar energetic particle (SEP) event.

💡 Did You Know? For scientists to confidently link an ancient radiation spike to solar activity, both carbon-14 (in trees) and beryllium-10 (in ice cores) must spike in the same year across global records. When that happens, it points strongly to a solar origin rather than cosmic sources like supernovae or gamma-ray bursts—or localized atmospheric effects like lightning or terrestrial radiation.

These particles—primarily high-energy protons and other charged particles from the Sun—are hurled toward Earth by intense solar activity. When they collide with atoms in our upper atmosphere, they trigger nuclear reactions that produce cosmogenic isotopes like carbon-14 (stored in trees) and beryllium-10 (stored in ice). Radiometric dating—measuring the decay of radioactive isotopes—allows researchers to estimate the age of materials. In this case, it helps pinpoint the year of the event alongside dendrochronology (tree-ring analysis).

Ice cores are like natural time capsules: layers of snow accumulate and compress into ice year after year, trapping traces of the atmosphere within them. Volcanic eruptions leave distinctive ash layers in these cores, which scientists can cross-reference with historical eruption records to accurately date the surrounding ice layers. Though not quite as precise as tree rings, ice cores can provide a remarkably reliable timeline going back hundreds of thousands of years.

The study also highlighted how cosmic rays from beyond our solar system—such as those from supernovae or black holes—continuously contribute to the radioactive signature in Earth’s biosphere. But it’s the solar-origin events, like this one, that cause dramatic one-year spikes. Though rare, they can have profound effects on our planet’s magnetic environment and could severely impact modern technology if they occurred today.

Detecting and Predicting Auroras

The Kp Index tracks geomagnetic activity (higher = more visible auroras, even farther from the poles).

Aurora forecasting tools:

• NOAA Space Weather Prediction Center
• My Aurora Forecast App
• Stellarium Planetarium App

These tools were listed on the final slide of Dr. Metcalfe’s presentation, offering easy ways to track aurora forecasts and geomagnetic activity.

Dr. Metcalfe saw her first aurora last May—and mentioned that they’re often gray to the naked eye, something that surprised many of us who expected vivid colors like in photographs. Cameras pick up more color than our night vision can.

Club Moments and Curious Questions

There was some great discussion about how auroras can look very different depending on the magnetic field conditions—some reported fog-like glows or horizontal bands instead of the classic curtain effect.

Dr. Metcalfe explained that auroras come in many forms based on how Earth’s magnetic field is distorted at that time.

Some other highlights:

• Dr. Metcalfe shared a hilarious story about mistaking casino lights for aurora.
• Someone asked about “Steve,” a newly discovered auroral phenomenon.
• Another recalled barium experiments in the 1960s that created rainbow-like clouds.

Some members even spotted a Kp-9 aurora right here in May 2024. Club President Paul expressed eternal gratitude for the late night phone call from a fellow member that alerted him to it.

Still Glowing Questions

Of course, there’s still plenty we don’t know. Here are a few of the lingering questions that came up—or are still bouncing around in my head:

• Why did that May 1921 storm happen near a solar minimum?
• What exactly is STEVE made of?
• Are there auroras on other planets, and if so, do they look like ours?
• And seriously—how does the Sun manage all this chaos without exploding?

Final Thoughts

Auroras are beautiful, mysterious, and deeply tied to both ancient wonder and cutting-edge science. They’re one of nature’s most spectacular shows.

And remember—the 11-year solar peak is happening right now. So if you’ve ever dreamed of seeing one, in the words of Janis Joplin: “Get it while you can.”

So keep your eyes on the sky—you just might catch one. And if you do, double-check it’s not a casino spotlight first.

Stay curious, and happy aurora hunting!