There are few sights more stunning in the night sky than the northern lights, but that shimmering curtain of light may become more difficult to enjoy if a new study proves to be accurate.
Published in the journal Scientific Reports, researchers charted the ebb and flow of sunspots and solar wind activity across the past 400 years, and based on that data, they predict the sun is about to enter a period of very limited sunspot and solar wind activity, the likes of which we haven't experienced since the start of the 1700s.
And a calmer-than-typical sun may have a sizable effect on not just the northern lights, but on the whole solar system.
What do those shimmering colors mean?
The northern (and southern) lights occur when gaseous particles in the Earth's atmosphere and charged particles from the sun, swept across space on solar winds, collide with one another. Different gases create different colors, and these different gases are located at different altitudes in the sky. The most common green northern lights occur with oxygen particles just 60 miles above the Earth, while the red in the northern lights is still oxygen, it's about 200 miles above the Earth. If you see blue northern lights, it's actually nitrogen, not oxygen, interacting with particles from the sun.
And that's where Earth comes into the equation. The sun's part is supplying electrons and photons that escape its atmosphere as the sun rotates. These particles travel along solar winds and eventually arrive to Earth. Most of the particles get bounced off thanks to Earth's magnetic field, but since the planet's magnetic field is weaker at and around the poles, the result are the northern lights.
We can predict solar wind activity based on how often sunspots form, and the more sunspots we see, the more active the sun itself is. However, without much in the way of solar wind activity, the northern lights become a limited engagement event.
"The northern lights phenomenon would become a natural show exclusive to the polar regions, due to a lack of solar wind forces that often make it visible at lower latitudes," according to Mathew Owens, from the University of Reading's Meteorology Department and the study's lead researcher.
Beyond the lights
Less solar activity has wider implications than just making the northern lights visible only to polar bears.
Remember Earth's magnetic field? The one that bounces off those solar particles? It responds to the ebb and flow of solar activity because it is, in part, created by solar wind. So as the sun enters a calm period, that magnetosphere shrinks. A smaller magnetosphere means that there's less potential protection from any intense solar activity that may happen.
"As the sun becomes less active, sunspots and coronal ejections will become less frequent," Owen explained. "However, if a mass ejection did hit the Earth, it could be even more damaging to the electronic devices on which society is now so dependent."
So, not a great situation for our cellphones and GPS devices, but with a less active sun, the chances of such an ejection are lower than they would be otherwise.
However, a calmer sun is more than just an Earth issue; it effects the whole solar system. Solar wind pushes out plasma from the sun well beyond Pluto, and this plasma creates a kind of bubble called the heliosphere that acts as a barrier against various interstellar cosmic rays produced by things like supernovae. Without the heliosphere, there'd be more cosmic radiation in our solar system, and if there's less solar wind pushing out plasma, that means the heliosphere could shrink.
"If the decline in sunspots continues at this rate, and data from the past suggests that it will, we could see these changes occurring as early as the next few decades," according to Mike Lockwood, who also worked on the study.