The Poetic Science of the Aurora Borealis
“And now commenced a display which baffles all description.”
By Maria Popova
On the evening of February 19, 1852, a scientist at the New Haven station of the nascent telegraph witnessed something extraordinary:
A blue line appeared upon the paper, which gradually grew darker and larger, until a flame of fire followed the pen, and burned through a dozen thicknesses of the prepared paper. The paper was set on fire by the flame, and produced considerable smoke. The current then subsided as gradually as it came on, until it entirely disappeared, and was then succeeded by a negative current, which bleached instead of colored, the paper; this also gradually increased, until, as with the positive current, it burned the paper, and then subsided, to be followed by the positive current.
The early telegraph was an electro-chemical technology that used a current passing through chemically coated paper to record a message from a faraway station. Lightning storms and other electrical disturbances were a known interference — a current of normal electricity would emit a bright spark while passing from the stylus to the moistened paper, but it would not set it aflame and would produce no color.
This was something else entirely.
It came in waves of varying intensity all throughout the evening, interpolating between positive and negative current with each wave.
Scientists knew of only one phenomenon in nature that corresponds to this pattern: the Aurora Borealis.
More than two millennia earlier, despite never having traveled far enough north from his Mediterranean home to witness this spectacle of the higher latitudes, Aristotle had described the phenomenon in his book on meteorology. An even more detailed depiction comes to us from Seneca, also captive to the lower latitudes his whole life, who described the northern lights in his Natural Questions, calling them Chasmata — chasms, rifts, gapings — of the sky:
Like a crown encircling the inner part of the fiery sky, there is a recess like the open mouth of a cave… A stretch of the sky seems to have receded and, gaping open, displays flames deep down. These all come in many colors: some are a very intense red; some have a weak, pale flame; some have a bright light; some pulsate; some are a uniform yellow with no discharges or rays emerging… The sky is seen to burn, the glow of which is occasionally so high it may be seen amongst the stars themselves, sometimes so near the ground that it assumes the form of distant fire.
In 1865, a decade and a half after he published Moby-Dick, Herman Melville was moved to commemorate the peaceful disbanding of the Civil War armies with the lush symbolism of the northern lights:
by Herman Melville
What power disbands the Northern Lights
After their steely play?
The lonely watcher feels an awe
Of Nature’s sway,
As when appearing,
He marked their flashed uprearing
In the cold gloom —
Retreatings and advancings,
(Like dallyings of doom),
Transitions and enhancings,
And bloody ray.
The phantom-host has faded quite,
Splendor and Terror gone —
Portent or promise — and gives way
To pale, meek Dawn;
The coming, going,
Alike in wonder showing —
Alike the God,
Decreeing and commanding
The million blades that glowed,
The muster and disbanding —
Midnight and Morn.
For as long as human animals have roamed the higher latitudes of the Northern hemisphere, the flaming dance of the sky has struck awe and wonder in the soul. But for the vast majority of the history of our species, it had no official name, appearing in various mythologies and early works of natural philosophy in various linguistic guises and poetic exultations.
The Aurora Borealis was christened by an improbable admirer — not Galileo, to whom the term is often misattributed, but the young French priest, philosopher, astronomer, and mathematician Pierre Gassendi (January 22, 1592–October 24, 1655) — the first human being to witness the transit of another planet (Mercury) across the face of the Sun.
A lecturer in Aristotelean philosophy and an expert in sunspots — miniature blackenings of the Sun’s photosphere due to drops in surface temperature caused by magnetic flux — Gassendi had long been captivated by Aristotle’s description of the northern lights and yearned to see them for himself, to savor their magic and work out their science, suspecting a correlation between sunspot activity and aurora sightings.
In 1621, he set out to put himself in the path of wonder and headed north. Chance favored him — this was one of the most active periods of auroral activity ever recorded; beginning just a few years later, the northern lights would slip into a long coma, not to shine again for nearly a century.
What the 29-year-old Gassendi witnessed seemed nothing less than the work of some cosmic god. He took it upon himself to name the nameless wonder, and it was only fitting that it bear a divine name: He chose Aurora, after the Roman goddess of dawn, and Borealis, after Boreas — the Greek god of the North wind.
Reasoning that this phenomenon takes place high above ground and only appears near the cold polar regions, Gassendi deduced a cause kindred to that of parhelia, or sundogs — bursts of light that typically appear in pairs around 22° to the left and right of the Sun, caused by ice crystals in the atmosphere refracting sunlight.
While his hypothesis was not entirely correct, it was the first robust scientific effort to discern a cause, and the closest any human being had come to an explanation since the dawn of our species.
It wasn’t until a century and a half after Gassendi’s death that the polymathic English “natural philosopher” Henry Cavendish — who lived in an epoch before the word scientist was coined — made measurable observations in 1790, estimating that aurora light is produced between 100 and 130 kilometers above ground. More than a century later, in 1902, the Norwegian physicist Kristian Birkeland performed an experiment with a magnetized model of Earth — a sphere known as terrella, Latin for “little Earth” — which he placed inside a vacuum chamber and showered with streams of the newly discovered electron. He watched with pleasure as the magnetic fields of the terrella steered the electrons toward its poles, illuminating the true cause of the northern lights — charged particles flowing through the gas of the upper atmosphere. It took more than half a century, until 1954, for actual electrons to be observed in the Aurora Borealis by detectors aboard a rocket launched into the polar skies.
And so it was pieced all together, this symphony of wonder generations in the composition: Auroras are caused by fluctuations in the Sun’s corona that send gusts of solar wind across the austere blackness of empty space, rippling through Earth’s magnetosphere. Magnetized by the solar wind, particles in the upper atmosphere above both poles — which is dominated by oxygen and nitrogen — grow excited, absorbing energy so that electrons jump from a lower to a higher state, or become ionized, losing an electron.
Because each element absorbs light from a different portion of the spectrum, and because its absorption pattern changes as atoms grow excited or ionized, we see bands of otherworldly light — the same electrochemistry by which neon lights work and television screens fluoresce. Oxygen — the dominant atmospheric gas — takes on the mid-range wavelengths of green (557.7 nm), slipping toward rose-red (630.0 nm) as it grows excited; ionized nitrogen colors the sky with the shorter wavelengths of blue and purple, while excited nitrogen blazes crimson. And so aurorae are primarily green, with swirls of pink and red toward the top, more prominent the more magnetic activity there is.
During particularly ferocious magnetic storms, the range of auroral activity, known as the aurora oval, widens as Earth’s atmosphere expands, sending those luminous colors higher and higher into the sky and farther and farther away from the poles, so that aurorae become visible at lower latitudes. As the excited nitrogen and low-density oxygen rise with their rosy hues, aurorae seen in lower latitudes tend to be dominated by red rather than green — so much so that a Roman emperor had once dispatched an army to aid a colony seemingly in flames, only to discover an apparition in the sky.
In the late summer of 1859, aurorae blazed across the skies of New York and California, Jamaica and Rome — the product of the most intense geomagnetic storm in recorded history, known as the Carrington Event, after the British astronomer Richard Christopher Carrington, who observed the solar flare that sparked it; it was the first recorded observation of a soar flare — a dramatic eruption of electromagnetic radiation in a concerted spot of the Sun’s atmosphere, which foments ferocious solar wind.
Because photography was still young then, and because the grandeur of the aurora naturally belongs in the category of the unphotographable, what delivered the spectacle to those not lucky enough to have witnessed it were not images but lyrical narrative accounts — the mind’s eye, enchanted and rendered awestruck by the evocative power of words.
One particularly wonderful account, far surpassing any possible photograph in detail and nuance of image, appeared in a small-town paper in Alabama, doing for the aurora borealis what Annie Dillard did for the eclipse, or Virginia Woolf:
At 1 o’clock… the whole atmosphere to the South was filled with greenish white masses of light resembling smoke, from a rapidly burning fire, or cumulo stratus clouds in a state of rapid motion from west to east, for which indeed they were first taken. But they were perfectly transparent, small stars being plainly visible through the largest of them. They retained the appearance of clouds only a short time — soon collecting near the zenith and assuming more brilliant hues. And now commenced a display which baffles all description: the light gathering to a focus, assuming the most fantastical forms, exhibiting the most eccentric motions — dispersing and recollecting with a rapidity that was almost bewildering, and a beauty that cannot be described. Several times a scroll or wave of white light, like a flag, would roll away from the brightest of the foci… and slowly disappear…
On the horizon of the west was a bank of dark clouds, and where the arch came in contact with these, it was a deep red color; and indeed whenever and wherever a cloud, however small, appeared, there the light was of a deep red — where the sky was clear, pale green and white were the prevalent colors. The light was evidently behind and beyond the clouds, and the red color resembled the red of a cloudy sunset.
To the North the appearance was singular. The sky was perfectly clear, and of an intense metallic brilliancy, having a distinct greenish tinge; and though the source of the light was evidently in this quarter of the heavens no shapes or motions of light were visible there…
The light afforded by this aurora was so great, that small objets were distinctly visible at great distances. Fine newspaper print could be read in the open air [at night] and many persons mistaking it for daylight, arose and commenced their daily avocations before discovering their mistake. It nearly resembled the light of early dawn and threw no shadow. It continued, with varying brilliancy, till obscured by daylight.
What human beings have witnessed beyond the shallow reach of recorded history we shall never know, but we do know that a detailed description of a low-latitude aurora appears in the first chapter of the Biblical book of Ezekiel. In our own century, scientists have used historical records and modern tools to uncover that the Carrington Event was far from unique — our planet has long been spectator and subject to its star’s ionic dramas. In the last week of summer in 1770, an intense magnetic storm sent aurorae all the way to Japan. A century later, in early February 1872, another ferocious solar flare colored the skies of Egypt, the Caribbean, and even the southern portions of Africa with its swirling radiance. It is possible that Aristotle and Seneca did, after all, see aurorae first-hand.
In consonance with Nobel-winning physicist Richard Feynman’s poetic meditation on the relationship between knowledge and mystery, I feel that the science of it — this work of immense forces across immense distances, this work of the human imagination across a lineage of minds thirsting for truth — only magnifies the magic of the celestial spectacle. Suddenly, we are plunged into a dazzling awareness of our cosmic origins and our connection to one another, each of us a link in the unbroken chain of time going back to Gassendi, back to the first human animal who looked up at the storm of color and was stilled with awe, back to the Big Bang that produced the particles roiling in the night sky. Whenever we gasp at an aurora, our lungs inhale molecules of air made of atoms forged in the first stars, and we are left wonder-smitten by reality — the only way worth living.
Published November 19, 2022