For the Northern Lights, winter is coming, and in more ways than one.
Predicting the appearance of the Northern Lights has always been something of a dark art, but there are some general rules of thumb to follow if you want to watch displays of the aurora borealis this fall and winter.
Being on the look-out between 8 p.m. and 2 a.m. from mid-September to mid-March is critical, preferably from within the Arctic Circle (latitudes between 64 degrees to 70 degrees north should do it) to maximise your chances.
However, there are bigger forces at play that mean this season is the best chance you've got until the early to mid-2020s.
How bright the Northern Lights are depends on solar weather. Though we talk about seasons for Northern Lights viewing, they're happening all the time—you just can't see them during the day, or during the height of summer when twilight never really ends and it doesn't get dark enough.
Northern Lights are caused by sunspots (concentrations of magnetic field flux, if you must know), some as big as 100,000 miles wide. It's these that astronomers watch to predict if the Northern Lights will be strong.
The Sun has its own approximately 11-year cycle, during which the number of sunspots on its surface waxes and wanes.
The more sunspots, the more active the Sun is. The more solar flares, the stronger a solar storm and the more highly charged particles are spewed out into the Solar System as massive “coronal mass ejections,” some of which are in the direction of Earth, where our planet's magnetic field deflects them in such a way that they cause harmless, visual magnetic storms: the Northern Lights.
After a solar storm, it takes about two to three days for the particles—the space weather—to reach Earth and trigger Northern Lights around the north pole (and Southern Lights around the south pole, which are an exact mirror image), though for a really large solar storm it can take just a day.
When the Sun is at its most active, it's termed Solar Maximum, but unfortunately for Norther Lights-hunters, that occurred in June 2014. Since the Northern Lights displays peak for about two or three years before and after Solar Maximum, we're on the bubble.
A spotless Sun?
We're now winding down to Solar Minimum, which is predicted to occur around about 2020 or 2021, so you want to get to the Arctic Circle well before then. Like, now.
The last Solar Minimum in 2008 and 2009 saw scant sunspots on the surface of the Sun, and Northern Lights displays were poor. Although the exact length of the Solar Cycle does vary (the actual cycle can be completed in as little as nine years, or as many as 14 years), it's best to be pessimistic. Sunspots are already reducing, with June 2016 seeing two days of a completely spotless Sun for the first time time since 2011.
Peaks and troughs
Although auroras will always be around even at the troughs of a Solar Minimum, there are doom-merchants that think we could we tumbling to a particularly pathetic show from the Sun over the next few decades. Let's just hope we're not headed for another Maunder Solar Minimum, a “prolonged sunspot minimum” period that occurred between 1645 and 1715, when astronomers recorded very few sunspots.
That's how some ice ages start, which for a bucket-list bagger standing in the freezing winds of the Arctic Circle, would be an ironic kick in the teeth. Still, all is not lost. A weaker sun means a weaker magnetic field, which means the little activity there is has a greater chance of getting into space and towards Earth.
Go north, and go soon, because for the Northern Lights, winter is coming.
Jamie Carter is a travel journalist, eclipse-chaser and author of “USA Eclipse 2017 Travel Guide” ebook and “A Stargazing Program for Beginners.”