Nordlys: a magic display of lights
Photo: “Green Energy” by Fredrik Broms / www.northernlightsphotography.no
Pål Brekke
Norwegian Space Center
For thousands of years people in the northern part of the world have marveled at the spectacular and fearful displays that occasionally light up the night sky. Every northern culture has legends about the aurora, passed down for generations.
During the Viking period, northern lights were referred to as reflections from dead maidens. The phenomenon was often referred to as a vengeful force. In ancient times, most people were afraid of the lights.
The Sámi people called it guovssahas, the light you can hear. Many people still argue that they can hear some crackling sounds—often synchronized with the movements of the aurora. Since sound waves cannot propagate in space it should be impossible for sound to travel down to the ground. Scientists are still working on explaining this phenomenon.
The Inuit people in the northernmost parts of Canada believed that the northern lights were created by spirits, which, dressed in the mystical light, were having fun while the sun was away, playing soccer with a walrus skull. The rapidly moving auroras were called the dance of death.
The Mandan Indians of North Dakota explained the lights as fires over which the great medicine men and warriors of northern nations simmered their dead enemies in enormous pots.
The Finnish name for the northern lights, revontulet, is associated with the arctic fox. According to a folk tale, an arctic fox is running far in the north and touching the mountains with its fur, so that sparks fly off into the sky as the northern lights.
One romantic conception found in Danish folklore is that these lights were due to a throng of swans flying so far to the north that they were caught in the ice. Each time they flapped their wings, they created reflections, which created the northern lights.
The Vikings first christened them “the northern lights.”
The first realistic description of auroras is found in the Norwegian chronicle The King’s Mirror from about A.D. 1230. It was originally written as a textbook, probably for the young King Magnus Lagabøte, by his father. At that time people thought the earth was flat and surrounded by oceans. One explanation was that the oceans were surrounded by fire and that auroras were the light from those fires reflected in the sky. Another possibility was that reflected sunlight from below the horizon illuminated the sky. A third explanation was fires in Greenland.
Sir Edmund Halley (1656-1742) suggested the aurora was caused by magnetic liquid evaporating from pores in the polar region and moving into the atmosphere along the magnetic field. Furthermore, he argued that the arc of the aurora did not point towards the geographic pole but rather toward the magnetic pole. The latter theory was correct and an important finding.
Norwegian scientist Kristian Birkeland (1867-1917) was the first to explain the real cause—that particles from the sun were sparking the northern lights. To prove his theory—which is still valid today—he built his own world in a glass box, electrified his model earth with a magnetic field, and showed how particles from the sun could ignite auroras. The particles were captured by the earth’s magnetic field and channeled towards the polar regions.
Photo courtesy of Pål Brekke
Kristian Birkeland with his Terella experiment that proved the modern understanding of the Northern Lights’ mechanism.
Many of Birkeland’s ideas were not confirmed until the Space Age. Since then, we have solved many of the aurora’s secrets.
The northern lights’ mechanism
When particles and magnetic fields from the sun reach Earth, they are deflected by an invisible shield—the Earth’s magnetic field, the magnetosphere.
The magnetic fields couple and disturb the magnetosphere. Some particles manage to enter the magnetosphere and are guided along magnetic field lines towards the poles. Eventually they collide with atoms in the Earth’s atmosphere.
These collisions usually take place between 80–300 km above ground. Here they cause oxygen and nitrogen to become excited and to emit light in much the same way as in fluorescent lights or in advertising neon signs. The result is a dazzling dance of green, blue, white, and red light in the sky forming in a ring-shaped area called the auroral oval.
Modern science
Today we study the northern lights from both ground and space. A large number of all-sky cameras and instruments study the phenomenon from many northern countries. These surveys include incoherent scatter radars, such as the large EISCAT antennas on Svalbard. Also on Svalbard sits the new Kjell Henriksen Observatory, opened in 2008, which is the largest aurora observatory of its kind with 30 dome-topped instrument rooms. Scientists around the world can remotely operate instruments here from their home institutions. What makes Svalbard special is that during daytime it is located right under the northern polar cusp. Here solar wind particles can enter directly into the atmosphere without being routed via the magnetic tail, as is the case for particle precipitation on the nightside.
Sounding rockets are also used to study the aurora. Launched from Fairbanks in Alaska, Svalbard, and Andøya they spear the aurora and can actually measure their physical properties. And from even higher up, satellites provide a global view of the auroral oval, the ring of light circling each geomagnetic pole.
Photo: Fredrik Broms
The little village of Grøtfjord in Northern Norway looks out to the open sea with a spectacular view of the northern skies.
Where to see the northern lights
The northern lights are different from other light phenomena in that they exhibit a variety of colors, structures, and movements.
Auroras are present within a zone of about 1,000 to 3,000 km from the magnetic poles, day and night during the entire year. However, auroras are only visible from the ground during clear, dark nights. Daylight will outshine the auroras.
If you are traveling north in quest of the auroras, go to the area around the aurora zone—a ring-shaped band where the chances of seeing the northern lights are highest. The aurora zone stretches across northern Scandinavia (Norway, Sweden, and Finland), over to Siberia in northern Russia, and then across Alaska and the northernmost parts of Canada to southern Greenland and Iceland. In these places you have the best chance of seeing auroras, and the best time to go is between mid September and mid March. Many of these areas are quite inaccessible due to lack of infrastructure and very low temperatures. North Norway has easy access, well-developed infrastructure for tourists, and a fairly mild climate. Furthermore, you will most likely see the lights every clear night.
If there is a gust in the solar wind—or a strong solar storm—the aurora will extend farther south. Sometimes they can be seen even south in Europe or the southern U.S.
How to predict the northern lights
Satellites observe the sun 24 hours a day, and scientists can detect eruptions that will produce strong northern lights. By monitoring this activity scientists can predict the strength and location of the aurora. These websites provide aurora forecasting:
• UNIS forecaster indicates where the aurora oval is located right now: kho.unis.no/Forecast.htm
• Spaceweather.com gives updates about upcoming auroras—and many amateurs are submitting images of the latest auroras: www.spaceweather.com
How to photograph the northern lights
Photographing northern lights is relatively easy, but for the best results some basic principles should be followed.
The best results are obtained with cameras that can be put in manual mode (M), where you can control shutter speed and aperture settings at the same time. This makes DSLR cameras best suited even if many compact cameras also will work.
When taking pictures of auroras a tripod is absolutely essential. Deactivate the flash and automatic settings. Pre-focus your lens at infinity and re-adjust if necessary. If you have a filter on your lens, remove it, as it usually causes undesirable concentric rings to appear on the images.
Fast lenses (f/2.8 or lower) with focal lengths of 10 to 35 mm are ideal. Whatever lens you have, set it to its lowest f-number and the ISO value fairly high. A good starting point is usually an exposure time between 8 and 30 seconds at ISO 800. At higher ISO values, image noise starts to become a problem, and finding a good balance between ISO value and exposure time is therefore crucial.
Pål Brekke is a solar physicist and a senior advisor at the Norwegian Space Centre. He worked as the Deputy SOHO Project Scientist for six years. He is also an adjunct professor at the University Center at Svalbard. His recent books Our Explosive Sun and Northern Lights: a Guide explore our stormy sun and the northern lights. He is also a producer of a new documentary about the Northern lights, Northern Lights: a Magic Experience, which is available in eight languages on DVD (both PAL and NTSC). More info: www.solarmax.no/Aurora/DVD.html.
This article originally appeared in the Dec. 4, 2015, issue of the Norwegian American Weekly.
