People across the UK, from the Shetland Islands to Somerset and from Norfolk to Northern Ireland, have been treated to a spectacular display of the aurora borealis or northern lights recently. But what is the cause of this beautiful phenomenon and why did it come so far south?
For thousands of years, people have associated the ghostly northern lights with the world of restless spirits. But in the last century, science has shown that aurorae originate in the area around our planet. The region of space close to Earth is called the magnetosphere. It is a mixture of atoms and molecules from the Earth’s upper atmosphere, broken up and heated by solar radiation (electromagnetic radiation emitted by the Sun).
The aurora borealis is created when these electrically charged particles rain down into the upper atmosphere. Most of the incoming particles that excite the light are electrons. As precipitation patterns shift, the shimmering aurora dances across the sky. Electrons are accelerated down the Earth’s magnetic field towards the polar regions.
The Sun emits several million tons of particles every second, creating the solar wind that constantly flows through our solar system. The solar wind drags the remnants of the Sun’s powerful magnetic field with it, bathing the planets in a magnetized vapor of particles smaller than atoms. The interactions between the solar wind and the Earth’s magnetosphere power the northern lights.
So what happened this week to drive aurorae to much lower latitudes than usual?
Towards the end of last week, scientists noticed a pair of coronal mass ejections (CMEs) on the Sun. A CME is an eruption of material from the Sun’s outer atmosphere (the corona). These explosive blasts can launch billions of tons of material in almost any direction, and Earth is usually hit a few times a month. As it happens, this pair of CMEs both shot Earth, the first leaving the Sun late on February 24th and the second late on February 25th.
Traveling at around 3 million kilometers per hour, the first CME took around 48 hours to travel the 150 million kilometers to Earth and slammed into the magnetosphere around 7pm (UK time) on Sunday, February 26. Impact of a billion tons of very high magnetization. , electrically-charged matter triggered a geomagnetic storm (a major disruption of the Earth’s magnetosphere). The electrons in the magnetosphere accelerated into the Earth’s atmosphere, triggering intense auroral displays that rapidly expanded much further toward the equator than usual.
Time was of the essence. The geomagnetic storm occurred in the early afternoon in the UK. Although it was dark, most people were awake and the weather was fine with clear skies across most of the country. As the geomagnetic storm intensified over the next few hours, pictures of the aurora from as far south as Kent filled social media timelines, prompting more people to scan the skies.
If the CME had arrived a few hours later, most people in the UK would have been in bed and probably missed the event. Cloudy weather would hide the show. But the timing was right and the famously unpredictable UK weather cooperated (for once).
By late Sunday afternoon, my phone was ringing. As a space scientist who researches the connections between the Sun and the Earth, I am often approached by the media when there is a hearing display across the UK.
As Monday morning broke, most of the media were running with stories about the previous night’s demonstration. Sure enough, most of the channels have found expert talking heads to talk about science. But for me, this event was different. Typically, the work of the “morning after” media involves answering an inevitable question: Will we see the northern lights again tonight?
Usually, the answer is “probably not.” In most cases, after 24 hours the intensity of the geomagnetic storm has diminished and the northern lights retreat from the UK towards their normal position on the edge of the arctic circle.
But this time, things were different. The second CME sent towards Earth was still on its way, so it was a rare opportunity for me to make an optimistic prediction. The second CME arrived after the first and engulfed the Earth in a flash around lunchtime on Monday, February 27. Weather conditions in the UK took a turn for the worse and cloud prevented many of the hopeful aurora seekers. But geomagnetic activity remained high for the second night in a row and people with clear skies were treated to another display of the northern lights.
When will we see them across Wales? It’s hard to say, but the prospects are improving. The Sun’s activity varies over an 11-year solar cycle, with CMEs (and aurora over the UK) most likely during the active parts of the cycle. Right now, solar activity is increasing as we move toward the next solar maximum, expected in 2025. Keep watching the skies—and social media.
Provided by An Comhrá
This article from The Conversation is republished under a Creative Commons license. Read the original article.
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