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In Depth

Northern Lights: More than just a pretty light show

About the author

Sarah Cruddas is a science journalist and broadcaster, based in London. She presents on Radio 4, works for various science TV shows and also writes for New Scientist. She tweets as @sarahcruddas

  • Greatest show on Earth
    The Northern Lights are one of nature’s most spectacular displays. How does it happen? Here are some aurora facts. (Copyright: Nasa)
  • Hi-energy collision
    Aurora form when energetic particles from the Sun hit Earth's magnetic field and are guided towards the atmosphere around the geomagnetic poles. (Copyright: Nasa)
  • Energy bursts
    Aurora are caused by solar activity, which goes through 11-year cycles. This year we are supposed to witness the peak of the current solar cycle. (Copyright: Nasa)
  • Rainbow of light
    The colours of aurora are dictated by what molecules solar wind particles collide with as they enter the earth’s atmosphere. (Copyright: Getty Images)
  • Seeing green
    Solar wind particles colliding with oxygen molecules typically produce green and yellow light. (Copyright: Getty Images)
  • Red sky at night…
    Solar wind particles colliding with nitrogen, on the other hand, produce reds, violets and sometimes blue. (Copyright: Getty Images)
  • Close encounters
    The International Space Station orbits at a similar altitude to aurora. Astronauts on board enjoy close-up views when the ISS flies through geomagnetic storms. (Copyright: Nasa)
  • Celestial sights
    Earth isn’t the only planet with aurora. Jupiter (seen here) and Saturn have aurora on both hemispheres, and aurora have been spotted on Uranus and Neptune. (Copyright: Nasa)
  • Alien worlds
    Recent studies may have found aurora outside our solar system – possibly a way to detect magnetospheres on exoplanets? (Copyright: Harvard-Smithsonian Center for Astrophysics)
  • See the light
    Back on Earth, the best chance of seeing the Northern Lights is within the Arctic Circle, in Alaska, Canada and northern Scandinavia. (Copyright: Getty Images)
Humans have been fascinated by this unpredictable, eerie light show for centuries. But it’s amazing how little we know about the science behind it.

The thermometer on the car is reading -22C. Outside, we are standing in snow up to my knees. We’re in a region called Inari in Finnish Lapland, inside the Arctic Circle, the nearest town is some kilometres to the south of us. You would be forgiven for thinking you were in Narnia, next to a frozen lake and surrounded by snow-topped pine trees. I can see more stars then I have ever seen before and some of the constellations such as Cassiopeia are difficult to spot, the sky is so free from light pollution. Which is supposedly the ideal place to do what I am doing; I’m one of a small group of people in search of the Northern Lights.

Our group is just one of many tours in this part of the world, eager to see the lights in all their glory. This type of tourism has become big business, several thousands of people choose to chase the lights every winter. Tour companies in regions such as Scandinavia and Alaska battle to find spots they say offer the best chance to see the elusive show. There are also cruises, and even chartered commercial flights, which travel to Arctic airspace to glimpse the phenomenon from above the clouds.

Humans have been fascinated by this unpredictable, eerie light show for centuries. It features in cave paintings in France thought to date back 30,000 years. Aristotle was captivated by the lights, calling them "jumping goats". Galileo described them as the dawn of the north, helping to coin the term aurora borealis. Europeans in the Middle Ages believed that the lights signified famine or war, while Native Americans saw them as gods dancing above the sky.

In this part of the world you don’t just find tour groups or trips with “hunters” chasing breaks in the cloud, more die-hard astronomy fans and photographers hire their own vehicles to chase the lights away from the tourists. “There is this sort of mystical quality to it, it really does pull you in," says astronomer and presenter of the Sky at Night, Pete Lawrence, who has photographed the lights around the world. I see what he means: on the horizon, I see a faint white haze starting to build, appearing initially like the Milky Way on a clear night. The beginning of the aurora slowly changes colour and form, taking over larger parts of the sky as the tour group eagerly set up their cameras.

Energy puzzle

But for such a well-known phenomenon, it’s amazing how little we know about the science beyond the basics. Thanks to work by Norwegian physicist Kristian Birkeland at the turn of the 20th Century, what we know is that auroral activity coincides with sunspots – darker, cooler regions of intense magnetic activity on the Sun’s surface. Birkeland said that currents flowing through the gas of the upper atmosphere caused the light show; in the same way that our modern-day neon lights work. “[Aurora] occur where energised particles coming from the sun interact with the Earth’s magnetic field,” says Lawrence.

What we also know is that aurora are inextricably linked with the activity of the Sun, and that solar activity appears to go through 11-year cycles. When it is at its most active, the so-called solar maximum, there are more sunspots present, and therefore more flares releasing powerful bursts of energy into space, as well as sprays of hot ionised gases, or plasma, that scientists call the solar wind. In theory, this should lead to bigger and brighter displays; however, it’s not quite that clear-cut. At the moment we are heading towards the peak of the current cycle, and Nasa had predicted that the northern lights would be the brightest and most intense for 50 years. But as it’s turned out this is a weak solar maximum, according to Mark Lester, who studies Solar Terrestrial Physics at the University of Leicester. And it’s not as simple to say we see less aurora during a solar minimum, either. There are two large, shifting ovals of auroral activity around the geomagnetic poles – one in the northern hemisphere, the other in the southern hemisphere (where the Southern Lights, or Aurora Australis can be seen). During a solar minimum what you get is aurora at a contracted aurora oval, so not at the place you imagine it to be at,” says Lester.

Auroras are elusive in other ways that fascinate scientists. For instance, where do the energised particles that cause the aurora actually come from. “Not directly from the sun. Lots of people get confused by this,” says Lester. As particles stream towards Earth, they hit the edge of the planet's magnetic “force field”, the magnetosphere. The field guides solar particles towards the poles, where they slam into the Earth's atmosphere and emit light. “You have to have interaction between the magnetosphere and the solar wind,” says Lester. “But this is not always what causes the brightness you see.” Several processes can cause the type of effect on particles that leads to aurora, which throws up bigger questions, like how energy flows through the solar system, how it interacts with Earth and other planets, and how the solar wind affects planets. “Although we understand the basic mechanisms, we don’t understand how it works dynamically,” says Dr Darren Wright, also at the University of Leicester.

There’s a growing need to answer these questions. As those who return home disappointed from a northern lights trip can testify, we can’t really predict auroras. From the vantage point of our own planet we are able to monitor the aurora in real time and combine with satellite measurements, such as those from the International Solar-Terrestrial Physics (ISTP) programme, an international effort run between Nasa, the European Space Agency, and Japan's Institute of Space and Astronautical Science. But despite the tremendous progress, aurora prediction doesn’t come with any guarantees.

This isn’t just an annoying inconvenience to hopeful travelers and stargazers. The more we become reliant on satellite technology, the more we need to forecast space weather more effectively, Sat-navs, such as those used to guide us to our location in Lapland rely on satellites, and these could potentially be damaged by the aurora. “If you get a big burst of activity from the sun, that can knock out some of the systems,” says Lawrence. A burst of solar activity can also affect many things here on Earth. In 1989, magnetic storms associated with an aurora caused a collapse of the Quebec power grid, leaving six million Canadians without electricity for hours. “If the aurora expand to lower latitudes than normal, “there could be problems to oil pipelines, transformers, power girds, anything with a metal conductor,” adds Lester.

Space lightshow

Astronauts are also at risk. In August 1972, as Apollo 16 had returned to Earth and Apollo 17 readied for its mission, there was a flare, which had astronauts been on the Moon at the time, could have been potentially lethal. Future missions to the Moon and Mars rely on understanding our sun and knowing how to protect astronauts. Deeper space exploration is also reliant on this knowledge. “For expensive space craft such as Nasa’s Juno mission to study Jupiter, there was a lot of research on how to protect instruments,” says Wright.

This is important because aurora are not unique to Earth, you can find them on planets like Jupiter and Saturn too. Aurora on Jupiter are a hundred times brighter than those found on Earth and are bigger than our entire planet. The reason we see similar displays on planets such as Jupiter is because they have magnetic fields, caused by having liquid metallic cores. Not all planets have aurora, though. Mars, for example, no longer has an active magnetosphere, and therefore no aurora, though according to Wright it could have done in the past. (The fact that Mars doesn’t have aurora also adds to the danger of any planned human mission to the planet; our magnetic field protects us from harmful solar radiation.)

What’s particularly interesting about Jupiter is that aurora are influenced by its moon IO, which provides charged particles to the gas giant’s magnetosphere. Scientists think similar processes could be responsible for radio emissions beyond our solar system. Researchers using the Low-Frequency Array radio telescope in the Netherlands recently observed emissions they say could be caused by powerful auroras. “Beefed up versions of the auroral processes on Jupiter are able to account for the radio emissions observed from certain ‘ultra cool dwarfs’ – failed stars which lie in between planets and stars in terms of mass,” said Jonathan Nichols at the University of Leicester, and lead researcher on the study.

If true, the implications of these findings could be enormous for aurora research. “You can learn about Earth by looking at Jupiter, and then compare Jupiter to more distant cosmic bodies,” says Nichols, “This is exciting because it helps us to understand how exoplanets behave.”

Astronomers are uncovering possible planets outside our galaxy at a tremendous rate – thanks to efforts like the Kepler Space Telescope the number of known exoplanets has risen past 900, with more than 2,700 candidates waiting to be confirmed. If we can detect radio emissions causing aurora on planets outside our solar system, this could reveal information about exoplanets that can’t currently be uncovered by other methods. It could tell us information such as the length of a planet’s day, how it interacts with its parent star and the strength of its magnetic field. There’s another, even more exciting possibility. Knowing how important the magnetic field is for protecting us on Earth, detecting aurora outside of our solar system could have implications with regards to identifying possible habitable planets.

Back in Inari, the group hurriedly take pictures as the intensity of the aurora display increases. Green and blue colours start to appear, and dance around the sky. A once-in-a-lifetime opportunity for many, the freezing temperatures, late night and expense seem to be worth it, as nature has played ball this time. However, as I look up at the glowing sky, I think about how the science behind what we are witnessing reaches beyond the seemingly simple explanation of what causes the display. Auroras are still a source a sense of wonder for scientists, as we are trying to learn more about our own planet and others elsewhere in the universe. Like the trip to see the Northern Lights forms part of many people’s life checklists, perhaps sometime in the future aurora hunting around the solar system could become an item to check off on an intergalactic bucket list.

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