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Skyglow Watching Days

"O'er all the widespread northern skies,
How glows and waves that heavenly light,
Where dome, and arch, and column rise
Magnificently bright!"

~ Stephen Greenleaf Bulfinch (1809 - 1870)

Have you ever seen the Northern Lights in the form of purple and green pillars and ribbons? If so, you may have witnessed the rare Skyglow, a cousin of the Aurora! As a result of the high resolution photography capture by amateur astronomers, scientists have been able to correlate the data from photos of these mysterious light pillars, first noted in 2016 with other measurements to define a mechanism for this display. Formally referred to as STEVE (Strong Thermal Emission Velocity Enhancement), Skyglow occurs outside the auroral zone as low-energy streams of free-moving, electrically excited particles bounce off neutral particles, creating friction and generating heat which is seen as a purple haze or ribbon, and sometimes with green picket fence streaks! 💜💚

A distinct phenomenon from the mechanism that produces the Aurora Borealis, STEVE (Strong Thermal Emission Velocity Enhancement), seen as ribbons or pillars of light in colors ranging from mauve to purple has recently been given a scientific explanation to account for the different conditions in which it forms.


In the Northern Hemisphere, this phenomenon is visible from areas farther south than a typical aurora, and it appears as a ribbon of pink, mauve, or purple light.  Sometimes, the purple pillar may even have a "picket fence" appearance, with green columns of light passing through the ribbon.   Additionally, STEVE can show up at the same time as an aurora does, which makes it even harder to figure out which is which. 


However, in a typical aurora, charged particles from the sun interact with Earth's oxygen and nitrogen molecules, exciting them into a high energy state which causes them to glow, usually as shimmering green streaks. 

 

But the STEVE phenomenon is visible from areas outside of the auroral zone and can occur in the absence of significant increases in solar charged particles.


Discovered in 2016 by citizen scientists in western Canada, scientists, further study shows that though STEVE is definitely created in the ionosphere, it is not an aurora, defined as light emissions caused by energetic electrons. Instead, low-energy streams of free-moving, electrically excited particles are bouncing off neutral particles, creating friction and generating heat seen as a pinkish or purple haze.  This skyglow can be considered analogous to the conditions creating the glow in an incandescent light bulb.


When this mysterious phenomenon was first spotted by amateur scientists over Canada, they first referred to it with  the amusingly ordinary name, Steve, as a reference to the 2006 animated comedy Over The Hedge, in which the woodland animal characters name a shrubbery Steve because they didn’t know what it was.  Elizabeth MacDonald, a space physicist at NASA’s Goddard Research Center and founder of the first citizen science network for the auroras, enjoyed the name, so her team turned it into the backronym STEVE, for Strong Thermal Emission Velocity Enhancement.


Designed by Carol A.L. Martin, this tartan illustrations the purple shades of the northern lights visible from her location, possibly a STEVE sighting. 


For more on the STEVE phenomenon, formerly known as skyglow, click the pillar of light against the Milky Way.