The aurora are looking back at us

Sometimes you wonder if the sky is staring back at you. Especially when you are under the seething aurora borealis in the ‘Auroral Zone’ which circles northern and southern latitudes.

Churning aurora over Kluane Lake, Yukon, September 2019 by the author

This is just one moment in the fast-and-slow movement of the aurora. What if you were a researcher and needed to look at a whole night, or whole months and years of aurora activity to find patterns of activity?

Watching thousands of hours of time lapse video won’t do — the time-series data needs a representation that can show a whole night at once.

Enter “the keogram.”

A keogram is a visualization of an entire night, from sunset to sunrise, read like a sentence from left to right. You can spot cloudy nights, nights with a bright moon, and nights with aurora activity. Here is a standard visible-light keogram of aurora activity from sunset to sunrise for one night:

A keogram of a single night’s aurora activity from sunset on the left through sunrise on the right

A keogram is generated from a single-pixel-wide slices of an all-sky-camera image. The slices run from the northern to southern horizon, taken at intervals through the night, and stacked left-to-right like the spines of books on a shelf. Here is how a single slice from a single moment of all-sky-camera imagery (from AuroraMAX) is inserted into that bookshelf:

All sky camera image of the aurora. The center slice of pixels north to south is sampled periodically
All sky camera image of the aurora. The center slice of pixels north to south is sampled periodically
Taking the center column of pixels from an all-sky-camera image of the night sky and placing it in time sequence in a keogram. The keogram is like the spines of books on a bookshelf — a quick overview

Here is a spotter’s guide to common keogram features:

Keograms allow quick recognition of different features of an evening’s sjy
Keograms allow quick recognition of different features of an evening’s sjy
Identifying the night’s activity from keograms

I’ve put together a demo web application that lets you explore years with of the Yellowknife night sky and aurora at a glance using the ‘magic’ of keogram spotting: https://www.jufaintermedia.com/demos/keogramindex/

It is quite easy to spot clouds, aurora, moonlight and auroral substorms when all the keograms for many nights are stacked:

A stack of keograms from several nights in a row. You can see the moon, clouds, and green of the aurora and quickly note which nights are worth further archival research (try it here: https://www.jufaintermedia.com/demos/keogramindex/)

Tapping on any keogram takes you from this “time traveller’s view” of the night skies to a camper’s eye view as if you were standing right under the aurora. It’s two side to data visualization: abstraction for parsing and search, and immersion for experiencing the story first-hand.

I am also experimenting with less utility-oriented representation of keograms. Wrapped in a polar transform, they look remarkably like a human iris — not space efficient, but is engaging and self-contained. Like human irises, each would be unique.

More reading

The AuroraMAX website, an amazing resource with years of all-sky-camera imagery from Yellowknife: https://www.asc-csa.gc.ca/eng/astronomy/auroramax/default.asp

Using this data, a keogram index and virtual planetarium interface is available as a demo here: https://www.jufaintermedia.com/demos/keogramindex/

I maintain how-to articles on aurora photography and aurora chasing at https://capturenorth.com/

Interactive developer for science and data outreach, github.com/jufa