The sky ribbon people called STEVE

STEVE above Childs Lake — Krista Trinder / NASA Goddard archive
Processed image. Krista Trinder’s view of STEVE and the Milky Way at Childs Lake, Manitoba. This is a stitched composite of 11 photographs, as recorded by the source.
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· Original image source · Image licence

Photographers noticed a pale purple ribbon that did not fit the familiar aurora. Sharing their images helped connect a public mystery with measurements passing overhead.

World: Earth
Location: Canada
Case date or period: 2016–present

The public noticed something worth following

Researchers describe how Alberta Aurora Chasers shared photographs of an unusual optical form in January 2016. These observers helped researchers recognise a feature in existing instrument data. The discovery grew from people comparing what they saw, rather than waiting for a catalogue entry.

A lucky overlap becomes evidence

In June 2016, ground-camera observations and a photographer’s images coincided with a Swarm satellite crossing. The spacecraft measured intense plasma flows and enhanced electron temperatures. Linking the public photographs to instrument observations made the phenomenon newly approachable.

Look for distinct structures

In these photographs, compare the long pale or purple arc with neighbouring green emissions and the ordinary star field. Later research examines the green “picket fence” separately. Beautiful images become especially valuable when observers preserve time, place, camera information and nearby views.

A hypothesis that changed with measurements

The researchers’ 2019 account explains that the photographers initially proposed a proton arc. Donovan rejected that suggestion because such an arc would be too faint for naked-eye observation. Later satellite analysis of another STEVE event found no evidence of the particle precipitation associated with ordinary aurora. These were successive tests of possible mechanisms, rather than identification by colour alone. The authors cautioned that public coverage had made their understanding sound more complete than it was.

Two photographs, different structures

The 2023 review by Nishimura and colleagues includes these Strathmore and Fort Frances photographs. Compare their exposures: ten seconds and four seconds. Bright green features accompany different portions of the pale arc. The authors caution that exposure time can hide finer structure, and ask how the two emissions connect. A photograph can preserve a striking pattern without settling its mechanism.