The thin ribbon is a rare and spectacular celestial phenomenon, but so much more than a mere aurora.
It isn’t often that skywatchers discover a new naked-eye phenomenon in astronomy, but it happened just a few years ago.
Aurora-watching observers in Alberta, Canada, routinely saw a unique purple/green light ribbon in the sky.
Formally discovered in late 2016, the new visual spectacle was named STEVE: strong thermal emission velocity enhancement.
Normally, aurorae are produced by the Sun’s charged particles striking the atoms in Earth’s upper atmosphere.
The solar wind particles get bent by Earth’s magnetic field, exciting and ionizing oxygen, nitrogen, and hydrogen.
When electrons recombine with ions, they cascade back down to lower energies, creating aurorae from their emission lines.
STEVE is distinct from this for multiple reasons.
1. STEVE is a thin ribbon that appears at lower latitudes than aurorae.
2. STEVE contains unique colors that aren’t created by aurorae.
3. Most importantly, aurorae are defined by charged particles falling onto our atmosphere; STEVE doesn’t have them.
Instead, STEVE is produced when charged particles collide much higher up, in Earth’s ionosphere.
These collisions cause tremendous heating and the emission of light, similar to incandescent bulb filaments.
STEVE is often accompanied by a true aurora: a green ‘picket fence,’ originating from electron precipitation.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.