The fireflies o’er the meadow In pulses come and go.
—JAMES RUSSELL LOWELL, “MIDNIGHT”
On a cool, clear July day I waited outside an apartment building in Hornsby, a suburb a few kilometers to the north of Sydney. The wheels of trains at the nearby station tapped out a staccato rhythm, and the traffic near the local mall was beginning to gel into a glacial, slow-moving mass. Finally, a car turned into the car park, accompanied by the muffled sounds of heavy metal music. I strongly suspected that Dr. Duane Hamacher, a researcher in Aboriginal astronomy, had arrived.
Wearing a leather jacket and tweed cap, Hamacher stepped out of the car, greeted me, and helped me find a place for my backpack in the trunk. We buckled in and headed northward to Ku-Ring-Gai Chase National Park, a 37,000-acre protected natural area where, I was assured, I would encounter evidence of ancient astronomical observing.
Within minutes, we had escaped the bustle of modern life and were winding along a park road bounded by gray sandstone rocks on one side and sweeping vistas on the other. The Sun filtered through the scribbly gum trees, illuminating the crisp leaf litter on the bushland floor. We pulled into a small car park that promised access to the Elvina Track, which would lead us part of the way to our destination. The rest of the route was a bit rough, I was told. Hamacher and I got out of the car, grabbed our packs, and began to hike up a wide, flat path.
Ku-Ring-Gai Chase National Park is situated on the large Hornsby Plateau, a great, ancient upwelling of sandstone and shale some 60 million years old. The citrus notes of eucalyptus, along with the songs of unfamiliar birds, lent an air of otherworldliness to the morning. I tried to imagine not just the astronomical observations, but also the lifestyle of the traditional Indigenous owners of Gadigal Country tens of thousands of years ago.
At a seemingly random spot on the trail, Hamacher abruptly left the marked path and began plowing through thick, crackling vegetation.
“Watch out for these,” he said, indicating a spiny branch at torso level. Too late. I had already snagged my arm on one.
We weaved and bobbed our way through the scrubby brush for a few minutes, each awkward step further convincing me that we were utterly lost. Finally, we emerged onto a shallow dome of sandstone.
I saw no astronomy.
Hamacher pointed to the right of my feet, and there, carved in the rock, were two familiar shapes. “Wallabies!” I exclaimed.
He gestured to the wide sweep of stone ahead. “Careful where you step. There are dozens of carvings on this rock.”
The ground was indeed covered with markings. My brain tried to separate the deliberate etchings from the odd erosion patterns. There was something fish-shaped. Carved. Several parallel lines seemed unusual, but were possibly natural. There was something elongated with stripes across it. Probably carved? A wavy outline of a person—definitely male. Two people—one male, one female—reaching up for what appeared to be a crescent Moon.
The lines were worn. In some cases, there was just a hint of a depression in the rock.
“How old are these?” I asked.
Hamacher explained that nobody knows. Five thousand years? Perhaps twice that. The English colonists had not taken great pains to communicate with the people in the area, most of whom were lost to disease and guns, both of which the English had brought to this corner of the continent.
“These are new, though,” he said disdainfully, looking down. Someone, possibly even a well-meaning someone, had scratched a fresh outline on one of the figures. “People seem to think they’re doing everyone a favor if they sharpen up the borders. That’s why they took down the sign pointing to this site.”
I now understood why it had been so important for Hamacher to get permission from Aboriginal rangers to bring me here, promising that we would do no damage.
We walked past a few more millennia-old carvings as I tried to wrap my brain around the fact that we were less than an hour’s drive from a city of 5 million.
“There she is,” Hamacher said, pointing.
And there she was. An enormous but slender emu in the most improbable position, her legs stretched far behind her bulbous body and her head stretched far in front. She was eight meters long from toe to beak, and as I paced the length of her figure, I saw absolutely nothing that immediately conveyed “astronomical calendar.”
Although it was not obvious to me, a twenty-first-century astronomer, the Indigenous Australians knew how to read it. The emu carving has such an unusual shape not because emus of the past were wildly different, but because it mimics the morphology of the Emu in the Sky. This “constellation” is one of those things that, once seen, can never be seen as anything else. Unlike Western constellations, which create a sort of dot-to-dot map from the stars, the Emu in the Sky is sculpted out of the dark dust lanes of the Milky Way Galaxy. Her dark head is the famous Coalsack Nebula, tucked just under one arm of Crux, the Southern Cross. Her ebony neck stretches past the bright Rigel Kentaurus (formerly known as Alpha Centauri, the nearest star system to our own), and her body encompasses part of Scorpius. Aptly, deep in her belly, but some 28,000 light-years away, is the center of the Milky Way Galaxy, which hosts an enormous gravitational bottomless pit.
But none of this would have been known to astronomers in millennia past.
According to Aboriginal astronomy scholars Cilla and Ray Norris, the Emu in the Sky “stands upright above her engraving only at the time each year when the emus lay their eggs.” At half a kilogram (about a pound) each, an emu egg is a veritable nutrient bomb. It is no wonder sky watchers took the time to etch this enormous shape with the correct orientation. The ancient rock carving was a link between the sky and the people. The heavens were a clock, reliable and enduring.
This reliability prompted Aristotle to pen, “In the whole range of time past, so far as our inherited records reach, no change appears to have taken place either in the whole scheme of the outermost heaven or in any of its proper parts.”
That I could see the same Emu traced out in the same dark, dusty nebulae of the Milky Way Galaxy in the twenty-first century is a testament to that endurance. The aptly named Coalsack Nebula—a sooty-looking expanse—lies about 450 light-years away and contains enough material to create over 3,000 Suns. Gravity might eventually get around to pulling together stars, but the Coalsack appears strangely reluctant to do so. The Emu’s head, seen by the Aboriginal people 60,000 years ago, will likely look the same 60,000 years hence. Aristotle’s heavens, in other words.
Hamacher and I pushed on, eventually coming to an overlook that afforded a sweeping view of Pittwater Bay. At the far tip of the land stands the Barrenjoey Lighthouse. I imagined it steadily sweeping its beam of light, alerting ships of the dangers of venturing too close. Hamacher told me that Aboriginal people had developed their own form of lighthouse here, communicating messages and positions from far away. Naturally, as I sat on the overlook, my thoughts turned from terrestrial lighthouses to the cosmic ones known as pulsars, and I wondered aloud if the original inhabitants had witnessed an explosive stellar death that led to a pulsar.
It was a question that Hamacher and others had pondered as well. Changes in the sky had often been recorded, but not in the way that Western science records things. “There is evidence in the oral traditions of the Kokatha and Ngarrindjeri peoples that they recognized the variability of the red stars Betelgeuse, Aldebaran, and Antares,” Hamacher explained. But since these records found their way into story lines rather than observation tables, their significance was overlooked until 2008, when graduate student Serena Fredrick first noted the parallels between sky stories and phenomena like Betelgeuse’s variability. In 2014, Hamacher and his colleague Trevor Leaman picked up Fredrick’s baton and ran farther.
Betelgeuse, a prominent star at the shoulder of Orion the hunter, does not shine steadily. It changes brightness as it swells and shrinks, brightening and dimming, over the course of about 400 days. The discovery of its variability is most commonly attributed to English astronomer Sir John Herschel, but Australia’s original observers had noticed its semiregular changes long before Herschel. At its maximum brightness, Betelgeuse outshines all the other stars in Orion. At its minimum, it is reduced to ruddy mediocrity.
In 2019, Betelgeuse took a sudden and unexpected nosedive. The dimming was imperceptible from one night to the next, but over the course of a season, it lost about 60% of its usual intensity. Once solidly in the stellar top ten list, it seemed to be fading into obscurity, and by early 2020, it was noticeably dimmer even to the untrained eye.
Despite the press coverage suggesting that this fading was a potential prelude to a spectacular and explosive death—something my students and I fervently prayed for on a daily basis—the only thing that made Betelgeuse’s decline impressive was the magnitude of it. It hit rock bottom in mid-February 2020 and then climbed back into its familiar rhythm once again. An obscuring blob of dust coughed out by the aging star was later determined to be the culprit. Not dead yet.
So what about other transient events in the sky? Betelgeuse might brighten and dim, but even after its 2019 free fall, it was still there. I asked Hamacher if he knew of any records, either in the rocks or in oral traditions, of one-time events. Something spectacular—say, the supernova of 1006.
There was no way Australia’s Indigenous peoples could have missed it. It was the most magnificent supernova in all of recorded history, an intense pinpoint of light so bright that you could read by it. SN 1006 blazed forth in early May of that year—in the Australian autumn—just above the shoulder of the Emu. (For those familiar with Western constellations, SN 1006 appeared southwest of the constellation Scorpius in the less well-known constellation of Lupus the hare.) On the night of the new star’s arrival, the crescent Moon would have quickly chased after the setting Sun, leaving the guest star to bathe this rocky overlook in a foreign, bright, blue-white light.
And not just the overlook. The entire continent of Australia and the whole world—at least all of it south of about 40 degrees North latitude—would have witnessed something noteworthy in the sky. For upward of three years (minus the span from October through November when it fell behind the Sun), the new star was visible, occasionally brightening and eventually dimming into the darkness from which it mysteriously sprang.
Where was its record among those whose latitude afforded them front-row seats?
The problem with understanding the information contained in rock art and story lines is twofold: (1) the information comes with virtually no context for those unfamiliar with traditional knowledge, and (2) there is quite a lot of it, and so interpreting the songs, the carvings, and the paintings can become a bit like interpreting the prophecies of Nostradamus. Scattered throughout Australia are literally thousands of sites with carvings or paintings, and much of their meaning was conveyed in symbolic narratives that have been tragically silenced. With so many centuries separating artist from observer, it is hard to divine exactly what the remaining art is telling us. Does a starburst pattern represent a supernova, a bright planetary conjunction, or a symbolic, more spiritual design with deep meaning to the artist?
For decades, I remained firmly convinced that a particular bit of Anasazi rock art in New Mexico’s Chaco Canyon represented the supernova event of 4 July 1054. Carl Sagan’s Cosmos had taught me that during my initial childhood taste of astronomy, and it likely triggered my intense yearning to see a supernova with my own eyes. “Supernovae are so amazing that people are compelled to literally carve the event in stone!” I thought.
I wanted to experience something that transformative.
But further work has cast doubt on the Chaco Canyon supernova interpretation. It might depict the event that blasted forth the Crab Nebula. Or it might not. Down the road, between Roswell and Las Cruces, New Mexico, a similarly cryptic petroglyph depicting a wavy starburst and a scorpion might represent the unrivaled explosion of the supernova of 1006. Or it might not.
Only a handful of potential supernova records exists in rock art around the world, and all the astronomical interpretations are speculative at best. A Bolivian petroglyph dating back about 10,000 years could represent the explosion that resulted in a wispy cloud known as the Vela supernova remnant, while a mural on a doorway in India is thought by some to mark a stellar explosion visible in 1604, which was, by comparison, practically yesterday.
It would be arrogant to assume that cultures around the world were unaware of these punctuated changes in the heavens. Instead, what the dearth of physical evidence of cosmic fireflies seems to reveal is the overriding importance of predictability. Within a year, most visible supernovae have winked out of our skies forever. Within a century, their appearance might be woven into a greater narrative about the courage of two fishermen brothers. And within a millennium, they might not be remembered at all. Betelgeuse has the advantage of staying power, its story attached to an ongoing phenomenon.
Still, we know that there was a brilliant, temporary event in the sky that began in 1006. This knowledge is owed in large part to the almost obsessive astronomical record-keeping in the Islamic and East Asian worlds. Make no mistake, though. The custom of noting every object in the sky had less to do with scientific rigor and more to do with astrological divination. Official sky watchers were compelled to provide detailed accounts of the behavior of every object in the heavens in a vain effort to make sense of the messy business of Earthbound humans. While it is true that we owe our existence to cosmic processes, it is the rare celestial event that has an impact on our day-to-day lives.
The records of SN 1006 can be found not in the durable rocks of Australia, but in the decidedly more fragile paper of the Islamic world. “I will now describe for you a spectacle that I saw at the beginning of my education,” wrote astrologer, astronomer, and physician Ali Ibn Ridwan in the eleventh century, as quoted by Bernard Goldstein. “The spectacle appeared in the zodiacal sign Scorpio in opposition to the Sun.”
He recounted vividly where the spectacle appeared and how its brilliance compared to that of known objects. The account is utterly unambiguous, bested only in details by numerous reports from China. In fact, it is the Chinese chronicles that reveal the stunning duration of the supernova’s visibility. SN 1006, by those records, was in the southern sky for over three years. All told, there are dozens of known accounts from China and Japan, a handful from the Arab world, and just two from Europe, where the new star would have barely peeked over the southern horizon.
And yet in all these detailed, occasionally embellished, ancient descriptions is nothing that explains what the spectacle of 1006 actually was.
There have been fewer than a dozen naked-eye supernovae in recorded history. Within a couple of generations of SN 1006, humanity was treated to a similar cosmic show in the constellation Taurus. That one happened on 4 July 1054, minus 6,500 or so years for light travel time, and the trigger was a single massive star that exhausted all its fuel sources and self-destructed. The explosion was so violent that the twisted, gaseous shrapnel is still racing away at over 1,000 kilometers per second. While it helps to have fancy astronomical instrumentation to measure this motion accurately, a time-lapse movie spanning a mere decade and a ruler will get you in the ballpark. In those ten years, a cosmic blink of an eye, the expansion is obvious. What is not so obvious is the little green man at its core.
There was a century-long pause between the 1054 supernova event and the next (1181), and then another four centuries before the next round of visible supernovae. The year 1572 was graced by one, as was 1604, a mere five years shy of the invention of the telescope. A supernova in our own Milky Way Galaxy has not appeared since. I tell my students that we are seriously overdue for another one, but this is a lie. Stars explode when physics dictates, not on some fixed galactic schedule. And in any event, the Milky Way has harbored other exploding stars, but its obscuring dust—the Emu itself—hides them from our view.
Looking deeper into history, the waters become more muddied. Chinese astronomers reported an event in the year 185 and another in 393, both of which have been declared bona fide supernovae through modern observational follow-ups. But there are a dozen more maybes, cold case files that might never see closure.
Astronomers David Green and F. Richard Stephenson suggested that it might be time to call it a day on finding ancient chronicles of exploding stars. “Looking to the future, it seems unlikely that records of additional supernovae . . . will come to light,” they explained. Science historians have sifted through the sources that they can get their hands on. As for the rest? “Even to access a small proportion of this material, which is scattered in numerous archives, would be extremely time-consuming.”
And what if we do run across an account of a “new star”? There is no guarantee that it describes an explosive death. A small, dense stellar corpse known as a white dwarf might suddenly and temporarily brighten if its partner encroaches upon its gravitational territory. This nonfatal flare-up is called a nova, an abbreviation of the Latin stella nova, which literally means “new star.” Although not nearly as dramatic or as final as its cousin the supernova, a sufficiently nearby nova would make keen observers take note.
Ferreting out historical novae is a bit of a challenge, though, because they simply aren’t as flashy as supernovae. A nova is a bit like a small cosmic belch. There is no epic bubble racing away from ground zero, no large-scale ionization that can be peered at centuries later with modern X-ray observatories. In a few weeks, the flare-up settles back down, and the white dwarf and its puffed-up companion go on as though nothing happened. That is, until the white dwarf reaches its limit.
Perhaps half a dozen verified naked-eye novae were recorded in the pre-telescopic era, mostly by Chinese and Japanese sky watchers, but there has been no systematic push to dig more deeply. “The observations of novae are of little value,” Stephenson states bluntly in a 1976 paper about historical novae and supernovae. But “observations of supernovae . . . must surely be regarded as among the most valuable legacies which the ancient world has bequeathed to modern science.”
Hamacher and I pushed back through the brushy vegetation, then across the stone, past the ancient Emu, past the wallaby sentries. If the written records of ancient astronomers are too much for modern scholars to slog through, how had he, Fredrick, and Leaman ferreted out evidence for variable stars in Aboriginal oral traditions? Fredrick’s master’s thesis explored the meanings of some 500 story lines, most of which have nothing to do with cosmic goings-on. It was only after spending years combing through narratives that mentioned anything in the sky and consulting with Aboriginal elders that Hamacher and Leaman were able to draw stronger conclusions about some of the less well-behaved objects like variable stars. But those are the recent stories. Tales from a millennium ago might still exist, but so far none irrefutably describe a bright new dot in the sky.
There are simply too many records to sift through. Too much data. Events that are too short-lived and too easily forgotten. These themes, as it turns out, are practically the hallmarks of studying temporary events in the universe.
“Of course,” Hamacher said. “There’s more to the transient universe than exploding stars and nova outbursts. Let me tell you about Collowgullouric War, which means the Wife of the Crow. But you probably know her better as Eta Carinae. Now there’s a hot mess.”
A hot mess, indeed. And it’s destined to become an even hotter, messier mess.
But let’s not go there just yet. Let’s find out more about how we got here.