A bright reddish ray shone in the sky over parts of Denmark at the end of March after a solar storm that stunned scientists with its intensity. The phenomenon in question was a red stable auroral arc (SAR) and was recorded by astrophotographer Ruslan Merzlyakov.
“On that night between the 23rd and 24th of March, Møns Klint was the only area in all of Denmark with clear skies, so naturally I wanted to try to capture the auroras,” Merzlyakov wrote. “Instead, I got this wonderful SAR.”
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When particles released by the Sun during solar flares and other phenomena reach Earth, they can form colorful aurora borealis. The auroral arc is not an aurora, and even less a stable phenomenon — the name is a “memory” of when the SARs were discovered by scientists, still with a misconception about the event.
The big difference is in the formation of auroras and SARs. While the aurora borealis is formed by interactions between particles from the Sun and gases in the atmosphere, the SAR comes from light emitted by oxygen molecules in Earth’s upper atmosphere, which have been heated by the system of electrical currents that surround our planet.
The current system surrounds the Earth’s magnetosphere (name of the area around our planet controlled by the magnetic field) and heats the gases in the upper atmosphere; thus, there is a glow that resembles that of the auroras, but which has a completely different origin. The color is the result of heating oxygen, the only gas heated during SAR.
SARs occur frequently, but because they are dimly bright, they are often overlooked. Coincidentally, this SAR was accompanied by one of the most intense geomagnetic storms in recent years, caused by a large coronal mass ejection. The storm was so intense that it weakened the magnetosphere, allowing more heat from the current system to reach the upper atmosphere, which made the arc easier to observe.
Source: Space Weather
