Aurora looking back at us!
Sometimes you wonder if the sky is staring back at you. Here is a data visualization I have been experimenting with that actually looks like the eye of the aurora:
These are 'keograms' - 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.
Keogram is made 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:
Here is a little spotter's guide to common features of a keogram
Aurora moving overhead from the north:
An auroral substorm starts in the southern horizon and quickly grows to fills the whole sky before dissipating:
Less common red aurora! These are seen when geomagnetic activity is quite high and are unusual in 2020 when the solar cycle is at a quiet point:
Unfortunately the aurora are above the clouds, so often obscuring clouds can be seen forming:
The bright moon will wash out the dimmer aurora features and appear as a bright slash of white:
During dawn and dusk, the ends of the keogram will start to show the sky brightening:
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:
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