Science of the Northern Lights Aurora Borealis
by Pål Brekke
Sir Edmund Halley suggested the aurora was caused by magnetic liquid evaporating from pores in the polar region and moving up in the atmosphere along the magnetic field and then creating the northern lights. Furthermore, he argued that the arc of the aurora did not point towards the geographic pole, but rather toward the magnetic pole, which is in a different location. The latter finding was correct and an important finding. The photo at the top of this post is taken by Pål Brekke.
The Norwegian scientist Kristian Olaf Birkeland, 1867-1917, was the first to explain the actual 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 its own magnetic field and showed how particles from the Sun could ignite auroras. The photo is courtesy of the University of Oslo. The particles were captured by the Earth’s magnetic field and channelled down towards the polar regions. Birkeland, his experiment and many facts about the northern lights are pictured on the Norwegian 200 kr bill. Despite the importance of this work, many of Birkeland’s ideas were not confirmed until the Space Age. Since then we have solved many of the aurora’s secrets.
What are the Northern Lights, Aurora Borealis?
When particles and magnetic fields from the Sun reach Earth, something strange happens. It’s as if they are deflected by an invisible shield – the Earth’s magnetic field – the magnetosphere. This illustration is courtesy of T. Abrahamsen.
The magnetic fields couple together and disturb the magnetosphere. Some particles are accelerated by changes in the Earth’s magnetic field and manage to enter the magnetosphere, being guided along the magnetic field lines towards the polar regions of the Earth. 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 atoms to become excited and to emit light in much the same ways 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 aurora oval.
Modern Observations and Measurements
Today we study the northern lights from both the ground and space. A large number of all-sky cameras and instruments are used to study the phenomenon from many northern countries. These surveys include incoherent scatter radars, such as the large EISCAT antennas on Svalbard, a Norwegian cluster of islands nearly as far north as Greenland’s northernmost shore. Also on Svalbard sits the new Kjell Henriksen Observatory, opened in 2008 and the largest aurora observatory of its kind, with 30 dome-topped instrument rooms. Here, scientists around the world can remotely operate their instruments from their home institution.
What makes Svalbard so special is its location, right under the northern polar cusp. Here solar wind particles can enter directly into the Earth’s atmosphere. Sounding rockets are also used to study the aurora. Launched from Fairbanks in Alaska, Svalbard, and Andøya (off mainland Norway) they spear the aurora and can actually measure its physical properties. And from even higher up, satellites provide a global view of the auroral oval, the ring of light circling each geomagnetic pole.
Where can you see the Northern Lights, Aurora Borealis?
The northern lights are impressive and different from all other light phenomena in that they exhibit an amazing variety of colours, structures, and movements. This photo is taken by Pål Brekke.
Auroras are present within a zone of about 1,000 to 3,000 km from the magnetic poles, both 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 travelling north in quest of the auroras, your best option will be to travel to the area around the aurora zone – a ring-shaped band where the chances of seeing the northern lights are highest (see image courtesy of NASA right). The aurora zone stretches across the northern part of Scandinavia (Norway, Sweden, and Finland), over to Siberia in northern Russia, and then across Alaska and the northernmost parts of Canada, and further across southern Greenland and Iceland. It is in these places that you have the best chances of seeing auroras, and the best time period to go is between mid-September and mid-March. Many of these areas are quite inaccessible to travellers due to lack of transport and have 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 northern lights every clear night. If there is a gust in the solar wind – or a strong solar storm – the northern lights will extend further south. Sometimes the aurora can be seen even further south in Europe or the southern states in USA.
Here is a Youtube video about the aurora
How can we predict the Northern Lights, Aurora Borealis
Several satellites are observing the Sun 24 hours a day and scientists can detect eruptions on the Sun that will produce strong Northern Lights. By monitoring the activity on the Sun every day scientists can predict the strength and the location of the aurora. Thus, by using the Internet you can find web pages that provide aurora forecasting.
UNIS forecaster indicates where the aurora oval is located right now: http://kho.unis.no/Forecast.htm
Spaceweather.com gives updates about upcoming auroras – and many amateurs are submitting images of the latest auroras: http://www.spaceweather.com
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 Centre 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”.
Pål says: ‘The Sun has fascinated me for many years. This is perhaps not so strange since I walked my first steps at the solar observatory at Harestua, just north of Oslo. My dad worked there then. I became fascinated by how dynamic the Sun is, how it has fascinated humans for thousands of years, and how it affects our technological society. During my studies at the University in Oslo, my advisors inspired me to spend time doing public outreach. So it was my interest for sharing knowledge about the mysteries of the Sun that led to my writing two books. The Sun is a perfect entrance to natural science, since it affects the Earth and humans in so many ways. Solar physics interacts with many other scientific fields, such as physics, chemistry, biology, and meteorology to mention a few.’