The 'Auroral oval' refers to a region surrounding the north and south geomagnetic poles that contain all Auroral observations at one point in time (Figure 3). The oval, which is shaped like a Frisbee with the center circular area cut out, expands and contracts with increasing and decreasing input of energy from the solar wind (See websites in Links). In general, there is a rather low chance of observing auroras over the poles. As one moves away from the North Pole towards lower latitudes the probability of observing auroras increases to a maximum around the border between the Northwest Territories and the rest of Canada. In Canada, aurora are best seen from the central Yukon, southeast through the Great Slave Lake area of the NWT, through northern Saskatchewan, Manitoba, and Ontario, and finally through central Quebec and Labrador. Moving further towards the equator the likelihood of observing auroras decreases. However, during large magnetic storms when a great deal of energy pours into the magnetosphere from the solar wind, aurora are sometimes seen at latitudes as low as Florida. In the NWT, tourists often visit Yellowknife and Fort Smith to view northern lights.

Figure 3. The auroral oval. The bulge is on the night-side of earth, which is the side facing away from the sun. This is also the tail-side of the magnetosphere.

Theoretically, we should be able to see the aurora 24 hours a day, 365 days a year, but there are two factors that play a role in its visibility. First, the orientation of the sun's magnetic field in relation to the earth's magnetic field influences the amount of energy from the solar wind that can penetrate into the magnetosphere. The second consideration is sunlight. Because of the brightness of the sun, seeing the aurora is very, difficult during the day.

Auroral displays are influenced by the solar cycle. Every eleven years, on average, the number of coronal mass ejections, which are huge bubbles of gas expel led by the sun into space, reach a maximum. Shortly after the maximum, that is early on in the declining phase, strong magnetic storms become more frequent. These storms generate aurora that are more dynamic than usual and occur closer to the equator. Simultaneously the polar cap - the region in the center of the oval where aurora are not present - expands southward. For example, the Auroral oval might push as far southward as the southern United States, with the polar cap as far south as Edmonton or Calgary. During these storms, the aurora are not visible in the NWT. After the storm, however, the polar cap shrinks and the aurora return to our area with a vengeance. At these times, the Auroral displays can be spectacular.

On a shorter scale, aurora tend to show a 27 day cycle, corresponding to the 27 days it takes the sun to make one rotation. If an observer witnesses a vivid aurora they should check again 27 days later and may be lucky enough to witness another dramatic display.

Click here for Tips for Viewing the Aurora.