Fantastic displays of the Aurora Borealis, or Northern Lights, have been known since antiquity. These shimmering curtains of spectral light may be a common sight if you live in Alaska or Northern Canada, but for most of us here in the lower states, they just aren’t that frequent. In fact, it’s estimated that only five percent of Earth’s inhabitants have seen an aurora. But don’t despair, because the tips on this page will help increase your chances of spotting the elusive lights.
Auroras are temporary disturbances in Earth’s magnetic field that are triggered from activity on the Sun. Fortunately, unlike our ancestors, we have the capability to know when to expect a major disturbance. We can find out with just a few computer keystokes.
Here’s what you do to get ready. First, you’ll need to bookmark a Web site that provides aurora predictions. The best way is to sign up for Sky & Telescope‘s AstroAlert service. Subscribe to the "Solar activity & auroras" alert. You will get occasional e-mail messages a day or two before significant magnetic storms are expected to occur. (You can cancel your subscription at any time.) You might also want to check out the Space Weather Bureau, which gives daily reports of geomagnetic activity and the probability of solar flares — the solar storms that trigger the magnetic disturbances on Earth. One other site, the University of Alaska Geophysical Institute, offers weekly auroral forecasts and photographs. The tip off for a pending aurora is a solar flare near the center of the Sun’s disk. It takes a day or two for the solar storm’s particles to travel through space and collide with Earth.
The best time to look for an aurora on any given night, unfortunately, is toward the middle of the night and into the morning (If you’re an early riser that’s okay!). It’s always best to look for a weak green glow low in the northern sky. But when big disturbances occur, the aurora can be seen much earlier in the evening and much higher in the sky. If a bright display occurs early in the evening, there is a good chance that another display will follow a couple of hours later. Its colors can vary from green to red, and you can see much shimmering.
There are so many shapes and forms of the aurora that they are likened to snowflakes – no two are alike. So it’s hard to say what you should expect to see. Most aurorae have a curtainlike or ribbonlike form. As the auroral activity increases, folds develop with the complexity and extent of the folds depending on the degree of activity. Robert Eather, a physicist who has studied auroras for 25 years, says these curtains can have five fundamental shapes:
- Arcs — Simple, slightly curved bands of light with smooth bottom edges.
- Bands — Continuous, but irregular lower edges, characterized by kinks or folds.
- Patches — Small isolated regions of glow.
- Veils — Extensive, uniform glows covering an appreciable fraction of the sky.
- Rays — Vertical shafts of light.
Auroras can remain "quiet" or be nearly motionless for a fairly long time, or they may suddenly start to pulsate slowly. Some may flicker rapidly, changing their intensity five or 10 times per second! Occasionally you can see auroral "flames" – bursts of light that appear at the base of the aurora and move rapidly upward though the large curtain of light.
Though the aurorae appear to come near to the ground, the light originates high in the atmosphere. The lowest aurorae are about 100 kilometers or 62 miles above the ground, with the highest extending to 4 times that distance. This is much higher than clouds or the highest flying aircraft (besides the Space Shuttle).
Most aurorae that appear bright to the eye are difficult to capture on film. But it can be done if you have the proper equipment. You’ll need a simple 35-mm camera with a B (Bulb) setting (meaning you can keep the shutter open for extended periods of time), a cable release, a fast lens (a standard 50-mm, f/1.8 is fine), fast film with an ISO rating of at least 400 (800 to 1000 is even better), and a sturdy tripod.
First load the film and be sure to set the ISO setting on your camera to the film speed you’re using. Next, check the aperture setting (F/number) on the lens; the lowest number is what you want (such as "1.8" – not "16" or "22"). Turn the shutter speed dial to "B." Attach the camera to the tripod. Then finally connect the cable release. You are ready to go. Simply wind the film, point the camera at the aurora, press the lever on the cable release, lock it into position, and expose the film.
The length of the exposure will depend on two things: (1) the brightness of the background sky; do you live in a city with bright lights or the country with dark skies? and (2) the brightness of the aurora. I would suggest you "bracket" your exposures. That means take a series of photos ranging from 2 seconds to 60 seconds. You’ll have to be the judge of what exposure works best.
Finally, be sure to frame the photograph artistically. The best aurora photographs use some kind of foreground object for scale, such as the top of a house, or a tree. Be an artist and use the landscape and the aurora to capture the beauty of the moment.