The aurora is a beautiful, if hard to predict, phenomenon, occurring year-round.
In Alaska, summers are marked by extremely long days. Thus, only in the fall, winter and early spring is there enough darkness to allow a chance of seeing the northern lights.
How to See Aurora
Aurora viewing takes luck and patience.
In general, viewing is more likely the farther north you are, as the phenomenon takes place around the poles. Sometimes aurora is active as far south as the upper midwest of the United States, but this is rare.
In Denali National Park, skies are dark enough from roughly mid-August to mid-April for good chances of aurora viewing. Visitors traveling to the park in June or July will certainly not see aurora, as it is far too bright that time of year.
Consult one of several aurora forecasts to get an idea of how likely it is you'll see aurora (note: these forecasts, like weather forecasts, can be changeable and are looking mainly at the short-term, e.g., 3 days to a week).
The Science of AuroraThe aurora borealis (Northern Lights) occurs when a coronal mass ejection (CME), a massive burst of solar wind and magnetic fields, interacts with elements in the earth's atmosphere. Coronal mass ejections are often associated with other forms of solar activity, most notably solar flares. Near solar maxima the sun produces about three CMEs every day, whereas near solar minima there is about one CME every five days. Solar winds stream away from the sun at speeds of about 1 million miles per hour and reach the earth roughly 40 hours after leaving the sun. As the electrons enter the earth's upper atmosphere, they will encounter atoms of oxygen and nitrogen at altitudes from 20 to 200 miles above the earth's surface. The color of the aurora depends on which atom is struck, and the altitude of the meeting.
- Green - oxygen, up to 150 miles in altitude
- Red - oxygen, above 150 miles in altitude
- Blue - nitrogen, up to 60 miles in altitude
- Purple/violet - nitrogen, above 60 miles in altitude
The auroras generally occur along the auroral ovals, which center on the magnetic poles and roughly correspond with the Arctic and Antarctic circles. The lights can be visible at lower latitudes when solar activity is high.