Rare blood-red arc of light shines in the Scandinavian sky. What is it?

A colse-up of the red light streaking across the night sky. — The band of sunshine illuminated the skies above Denmark on March 23. (Picture credit score: Ruslan Merzlyakov)

A vibrant purple streak of sunshine appeared within the sky above components of Scandinavia final week after a shock photo voltaic storm smashed into Earth and triggered beautiful auroras throughout the planet. However the vibrant purple band was not an aurora — it was one thing a lot rarer.

The streak, which appeared as a river of hazy purple mild that stretched all the best way throughout the evening sky, was most prominently seen above Denmark. Astrophotographer Ruslan Merzlyakov (opens in new tab) snapped a spectacular shot (opens in new tab) of the peculiar mild present on March 23 above Møns Klint, a set of limestone cliffs on the Danish island of Møn within the Baltic Sea.

The bizarre phenomenon is called a steady auroral purple arc (SAR), however regardless of the title, it isn’t an aurora or significantly steady, in response to Spaceweather.com (opens in new tab). As a substitute, the sunshine is emitted by oxygen molecules within the higher environment which have change into superheated by Earth’s ring present system, a large loop of electrical present that surrounds our planet.

The SAR coincided with the strongest geomagnetic storm to hit Earth for six years, which was triggered by a shock coronal mass ejection — a gargantuan, fast-moving blob of plasma and magnetic subject launched from the solar — that was spat out of a large gap within the solar wider than 20 Earths.

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The SAR shines above limestone cliffs in Denmark.

{A photograph} of the SAR within the evening sky above Møns Klint on March 23. (Picture credit score: Ruslan Merzlyakov)

Throughout auroras, extremely energetic particles from photo voltaic storms and photo voltaic wind bypass Earth’s magnetic subject, or magnetosphere, and excite molecules of gasoline within the higher environment. This creates swirling, multicolor lights that ebb and stream over time. The assorted colours of sunshine come from totally different atoms, which emit particular colours when excited.

Throughout SARs, vitality from the ring present system, which surrounds the magnetosphere, heats up the gasoline within the higher environment and makes it glow like an aurora. For unknown causes, solely oxygen is heated up throughout a SAR, which implies these phenomena all the time emit the very same shade of purple, in response to Spaceweather.com.

SARs really happen fairly incessantly, however they’re usually invisible to people as a result of they’re too faint and our eyes are poorly attuned to the wavelength of purple mild emitted by SARs, in response to Spaceweather.com. Huge streaks just like the one over Denmark solely change into seen when robust photo voltaic storms weaken the magnetosphere, which permits extra warmth from the ring present system to enter the higher environment.

The SAR over Denmark was not the one uncommon mild present noticed through the latest photo voltaic storm. The aurora-like phenomenon STEVE, a big ribbon of coloured mild that hangs within the sky for as much as an hour, was additionally seen throughout the USA and components of the UK.

There may be some proof that STEVE and SAR arcs are associated phenomena. In March 2015, skywatchers in New Zealand watched as a vibrant purple SAR slowly reworked right into a STEVE occasion over the course of about half an hour.

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