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STEVE – that’s Strong Thermal Emission Velocity Enhancement – isn’t your ordinary aurora. Featuring a lengthy purple arc and sometimes a green, picket fence structure, this peculiar lightshow is often clocked at latitudes far lower than your normal shimmering curtains of red and green. Compared to the northern lights, it is deeply puzzling. Scientists are still trying to work out what makes STEVE tick, and whether it is, or isn’t, an aurora.

In the days after STEVE’s existence was revealed in 2018, Michael Hunnekuhl, a laser physicist at Laser Zentrum Hannover in Germany and part-time aurora historian, was reading through some old papers by the late, great Carl Størmer, a Norwegian mathematician, astrophysicist and aurora hunter. By chance, he spied some curious observations Størmer made, of a feebly lit arc, hanging low and stretching across the sky. 

Flipping through more of Størmer’s reports, Hunnekuhl found several more descriptions just like this, and even a black-and-white photograph of one of these arcs. There was little doubt: these observations had to be of STEVE. But these reports weren’t a product of modern times. As reported in the journal Space Weather back in February, Hunnekuhl found entries dating as far back as 1911, a time when both auroral science and photographic technology were still in their infancy. 

STEVE may have been formally discovered by a team of scientists and aurora chasers in 2018, but thanks to this time-traveling quest, we now know that its been spotted for over a century. And STEVE has almost certainly been meandering across our world’s darkened skies since long before humanity made our evolutionary debut.

These observations “demonstrate that STEVE didn’t just start happening, which is comforting,” says Elizabeth MacDonald, space weather scientist at NASA’s Goddard Space Flight Center and co-author of the new study. But it’s also exciting to realize that what has been framed as a modern mystery is in fact a conundrum that has been captivating people since before the First World War.

Hannahbella Nel, an aurora photography guide not involved with the new study, first saw the faintly glowing arc a few years back in Jasper, Alberta, up in the Canadian Rockies. “There was suddenly this weird line coming over the mountain, going east to west, straight overhead and beyond,” she says. It looked a bit like an airplane’s contrail. With some long-exposure photographs, its milky purple hues emerged.

Prior to this sighting, she had teamed up with Alberta’s aurora chaser group, and they had all been talking about something called Steve, a strange arc in the night sky. Was her sighting of the elusive gentleman of which they spoke? 

The moniker of Steve was the brainchild of Chris Ratzlaff, the leader of the Alberta aurora chasers. This was a reference to a moment in Over The Hedge, an animated comedy from 2006, in which animals refer to a hedge as ‘Steve’ because they had no other name for it. 

MacDonald, the founder of Aurorasaurus – the first citizen science network for reporting aurora sightings – enjoyed the name so much that she turned it into the backronymic STEVE. In 2018, with some key data from a satellite that flew across a STEVE event, MacDonald co-authored a study with her scientific colleagues and aurora chaser confederates that described the lightshow as a new species of aurora. 

Ever since, scientists have tried their best to decode the physics of STEVE. It’s a real headscratcher, because it resembles your classic aurora in some ways, but not others. But despite the ongoing debate over its nature and classification, everyone agrees that STEVE appears in a weird place in the sky and behaves in very distinctive way. It’s perhaps surprising, then, that it was only spotted in the last decade.

Størmer, born in 1874, was an inexhaustible scientist for much of his lifetime. He calculated the trajectories of charged particles in Earth’s magnetic field, a key ingredient in auroral production. He conjured up the first camera able to take longer exposure images of the aurora. In 1930, he published the first atlas of the aurorae, a spotter’s guide to their many forms.

Between 1911 and 1944, using an array of aurora observations stations across Norway maintained by himself and a squad of assistants, Størmer was able to track auroral appearances across the country, recording accurate observations of their heights and other characteristics. At several points during this period, Størmer describes seeing several “feeble homogeneous arcs of great altitude.” 

MacDonald, co-author of the new study, says that these otherwise impressive arcs may have been described as ‘feeble’, because to the naked eye they can be dimly lit. But even without modern camera equipment to reveal its cryptic purple incandescence, it was clear that Størmer had been spotting STEVE. As well as being faint, these arcs appeared at just the right time, they were away from the main zone of aurora activity, were east-west oriented, and didn’t appear to be drifting to the south – all matching up with how we see STEVE today.

Hunnekuhl had enjoyed perusing through plenty of Størmer’s reports prior to 2018. “But when I read these papers, STEVE was completely unknown,” he says. Only after STEVE was revealed to the wider world that year did he realize, upon a second reading, that the Norwegian aurora hunter had been describing STEVE. 

Digging through old journals, Hunnekuhl found several more mentions of these feeble arcs. In 1911, one “stretched over the whole sky from horizon to horizon, from St. Petersburg to west of Scotland.” In 1933, one report described it as like the tail of a comet, one standing far from the remnant pulsating patches of an earlier aurora on the northern horizon.

Størmer wasn’t sure what to make of these arcs, but he suspected they were auroral forms. And although the truth is a little more complex, says Hunnekuhl, it is impressive that he managed to make such detailed observations of STEVE long before the space age began.

The unearthing of these observations is more of a historical curiosity than anything scientifically revelatory. But, says MacDonald, they underscore the importance of citizen scientist's efforts to untangle the mysteries of the many manifestations of space weather, of which the northern and southern lights are just one. 

After all, Størmer didn’t make these observations alone. As well as recruiting a team to help out, he also put the call out in newspapers and on the radio, imploring any members of the public with observations of the dancing lights to send them his way. This, says MacDonald, is comparable to how Aurorasaurus works today: it collects the observations of aurora chasers as they are uploaded online, either to a dedicated website, to an app or onto social media.

Hunnekuhl remains on the lookout for any additional historical observations of STEVE. A lingering puzzle, he says, is why he cannot find any observations in the scientific literature from around the time Størmer passed away in 1957 to the turn of the new millennium. There must have been observations during that half-century, but so far, he can’t find any.

Despite this informational gap, his dive through the past has been more successful than his endeavors in the present. “I’ve seen auroras a lot of times, but unfortunately not STEVE,” he says.

When the pandemic eases and the lockdowns are lifted, Hunnekuhl hopes to follow in the footsteps of Størmer, and finally go on a successful hunt of his own.