The Northern Lights or aurora borealis are a natural phenomenon that can paint the night sky with unearthly, surreal color. The Southern Lights or aurora australis also occur but are not as often observed.
The aurorae are caused by charged particles ejected from the sun. When these particles reach the earth, they collide with gas atoms and molecules in the earth’s upper atmosphere, energising them and creating a spectacular multi-coloured light show. Charged particles are affected by magnetic fields, so the Lights occur mainly at far northern or southern latitudes near the Earth’s magnetic poles.
The Lights look somewhat similar to a sunset in the sky at night, but appear occasionally in arcs or spirals usually following the earth’s magnetic field. They fairly often look like moving curtains of light, high in the sky. They are most often light green in color but often have a hint of pink. Strong eruptions also have violet and white colors. Red northern lights are rare, but are sometimes observed.
The Lights are generally fairly dim, but sometimes bright enough that reading a newspaper on a moonless night is possible. Both brightness and how far from the poles they are visible vary according to three factors: time of year, an 11-year cycle in solar activity, and solar storms. These are discussed in more detail later.
To observers at far-northern latitudes, the Lights are a frequent occurrence, but many who live in more temperate climates have never seen them, even though they are occasionally seen as far south as 35 degrees North latitude. This article will help you improve your chances of seeing the Lights if you journey north.
Light pollution around cities can mask a dim aurora display. Therefore, areas at least 30 km from cities are preferred for viewing. The trick is to get far enough from cities for good viewing (generally easy, since most northern areas are not heavily populated) without taking undue risks in a climate that can easily kill you.
Contrary to intuition, seeing the Northern Lights isn’t just a matter of heading north. The Lights occur mainly in a circular or elliptical band centered on the earth’s North Magnetic Pole, which is not at the same location as the North Geographic Pole. The exact location of the North Magnetic Pole varies from year to year, sometimes by tens of miles. The pole has been moving north for a few years and is now near Ellesmere Island in the nearly uninhabited far north of Canada. As a consequence, the advantages of being on the “right side” of the earth are not as pronounced as they were some years ago but even today there’s a slight North American bias in your chance of seeing the Lights.
Auroral displays aren’t strongest at the pole; the band of greatest activity is offset from the Magnetic Pole by 20 degrees or so; the magnetic lines of force are curved and the curvature creates the offset. The Northern Lights oval, meaning the area with the highest probability of seeing the Lights, covers most of Alaska, northern parts of Canada, the southern half of Greenland, Iceland, northern Norway and the northernmost areas of Sweden and Finland, as well as the western half of the Russian north. There is a similar oval in the South; see the photo.
Regions such as the central and southern parts of the Nordic countries, southern Canada, the north-central United States and Scotland also frequently see Northern Lights, but not as often as directly under the Northern Lights oval. Svalbard sees Northern Lights less often than Northern Scandinavia, but is a place to observe the fainter Day Northern Lights visible during waking hours in its long polar night.
That said, the actual latitudes of the Lights vary considerably. In times of high solar activity (more on that later), the Lights may be seen in North America at latitudes as low as 35 degrees North, meaning that all but the southernmost parts of the United States may get a display. The offset of the Pole keeps solar storms from benefiting Europe quite as strongly, but most of the countries of northern Europe will get displays during periods of solar storms.