First, the bad news for stargazers: Auroras are going dark in many parts of the world.
The number of these atmospheric light shows won't bottom out for several years, which means locations far from Earth's poles — such as the UK and northern continental US — may rarely if ever see the Northern Lights during that time. A study published earlier this year hints this dearth of auroras may last for decades.
But there's plenty of good news.
This coming dip in auroras is normal and expected, since it's tied to an 11-year cycle of solar activity that waxes and wanes. The sun just finished its last peak, called a solar maximum, in 2014, during which time researchers saw more sunspots, outbursts of solar particles, and auroras on Earth. Around solar minimum — around 2020 or 2021 — the reverse will happen.
"My personal prediction is that, over the next couple of years, we'll see a deep dive of solar activity into solar minimum, and fewer and fewer auroras will be seen," Doug Biesecker, a physicist at NOAA's Space Weather Prediction Center, told Business Insider.
This doesn't mean Earth will be devoid of auroras; anyone can make the trip to Arctic or Antarctic regions where auroras at night are persistent.
What's more, Business Insider has learned that the next solar maximum, set to occur around 2025, should be as strong or stronger than the one we just saw, bringing an eventual boost in the number of at lower-latitude auroras.
"There will be a ramp-up in solar activity a couple of years after solar minimum, and auroras should increase in frequency," Dean Pesnell, a solar physicist at NASA's Goddard Space Flight Center, told Business Insider.
Pesnell and his colleagues just submitted an as-yet unpublished study about this prediction, which is based on magnetic activity at the sun's poles. But Biesecker said that, based on the solar cycle's historical variability, "I could foresee a minimum as early as 2019 and a maximum as early as 2022."
The other good news? That decades-long void of auroras may never pan out.
The problem with predicting auroras
The sun constantly spews protons and other particles into space, and when they reach Earth, the planet's magnetic field grabs them and accelerates them toward the poles. As those particles slam into the atmosphere, they light up its gases like a neon light.
This happens every night close to Earth's poles, but strong outbursts of solar particles, like coronal mass ejections, can sometimes expand auroras down to states like Maine, North Dakota, New York, and even Colorado. And during solar maximum, such particle outbursts are more frequent (though not necessarily more intense).
"The places where the aurora is common, it's always going to be common. It's more a case of, 'is Colorado or North Dakota going to see it?'" Biesecker said. "Unfortunately, not as much during the solar minimum."
Earlier this year, a January study in Nature Scientific Reports hinted that the next dip in solar activity might last for decades. The researchers examined the past 400 years of solar activity records, and a computer model indicated Earth is in store for a few extra-boring 11-year solar cycles — and a related famine of auroras.
Yet both Biesecker and Pesnell said that long-term predictions are devilishly hard to trust.
Records older than 250 years aren't very reliable, Biesecker said. Even the past 250 years of observations of sunspots — the hallmarks of solar activity — are hard to trust in part because it's subjective; where one astronomer saw one solar blemish, another may have seen two. But solar physicists can always talk to whomever recorded previous observations.
"A new data point basically shows up once every 11 years. So very few people make it through two or three solar cycles in their research," Pesnell said. "They either go do something else, or they die."
Then there's the chaos of the sun itself.
A roughly 25-day-long rotation or "day" to the sun is what drives solar activity. This rotation gradually twists up the star's magnetic field lines like a rubber band, forming kinks that can lead to sunspots and solar outbursts. Yet these wild acrobatics on the surface don't appear to affect anything deep inside the sun — the pressure and density seems to totally counterract the influence of the surface.
This means the star doesn't have any kind of long-term "memory" scientists can exploit to predict its behavior more than a few years out.
"There's no compelling evidence that the sun 'knows' it's supposed to get weaker or return to normal at some future 11-year cycle," Biesecker said.
For now, the researchers said, all we can do is wait to see if there are as many or more auroras as the sun winds up toward its next maximum in 2025.
"Eight years from now," Pesnell said, "we'll know if our prediction was right."
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