A 360° fish-eye panorama of the odd isolated auroral arc that has become known as “Steve,” here across the bottom as a pink and white band, across the south, with the main auroral oval to the north at top, with its more normal oxygen green arc and upper red and magenta tints, also from atomic oxygen.
This demonstrates the relationship of the Steve arc to the main auroral oval — he is always equatorward of the main oval, and defines the southern limit of the display. Auroras are not seen south of the Steve arc.
The Steve arc seems to be a thermal emission from hot flowing gas rather than from precipitating electrons. But his origin and nature is still mysterious.
This night, September 27, 2017, the Steve arc appeared for only about 20 minutes, from 10:45 pm MDT pm, as the main display hit a lull inactivity. The display later grew to cover the sky with a post-sub-storm flickering display at the zenith and to the south. Steve is always well south of the main oval, and usually only when the main aurora is not very active.
The 6-day Moon is just setting at the bottom of the summer Milky Way. The Pleiades is rising at upper left. The Milky Way runs from northeast at upper left to southwest at lower right. The zenith is at centre.
This is a 360° panorama made of 6 segments, each with the Sigma 14mm f/1.8 lens at f/1.8 in portrait orienation, and at 60° spacings. Each exposure was 10 seconds at f/1.8 and ISO 2500 with the Nikon D750. Shot from home in southern Alberta on a mild September night. Stitched with PTGui with spherical projection.