In 1834, Canadian pioneer Catharine Parr Trail saw a strange sight in the sky: a “splendid pillar of pale greenish light”, which she described as wider at the base than at the peak, according to the December 2017 issue of The Journal of The RASC.
Trail was likely looking at a phenomenon known as the zodiacal light. We now know this strange light occurs when sunlight is reflected upon the dust grains floating between planets in the Solar System. It has been thought that this dust was the leftovers of our cosmic neighbourhood’s formation some 4.5 billion years ago, but there is new evidence showing the grains may come from Mars’ dust storms.
How do I see it?
Your best bet for seeing the zodiacal light is to pick a very dark location, ideally in a dark-sky site near your home. If you can’t get to a preserve, find as dark a location as you can — the more rural the observing spot and the further it is from city lights and pollution, the easier it will be to see the zodiacal light. Also pick a moonless night, or a night when the Moon is a small crescent.
While the timing of zodiacal light varies depending on how far or close you are from the Equator, a general rule of thumb is to go outside about 90 minutes after the Sun sets in the spring or before it rises in autumn. Allow your eyes 20 minutes to adjust to the darkness, and if you must use a light, make sure the light is heavily covered in red filters. You do not need to use binoculars or a telescope.
When your eyes are ready, look to the western sky and keep your eyes peeled for a very large cone or wedge-shaped pillar of light. If the sky is very dark, you may see the light stretch for several dozen degrees; in drier and desert-like regions, the light has been recorded going all the way to the eastern horizon.
Zodiacal light is best visible when the zodiac (which roughly follows the path of the planets) is at a steep angle to the horizon. In the northern hemisphere, that is after sunset in the spring, and before sunrise in the fall.
Photographing zodiacal light
The key to seeing this faint light is to let your camera lens gather as much data from the night sky as possible. Switch to the lowest f-stop possible (something like f/2.8) and set the ISO to at least 1600. Focus your camera lens on infinity, set your camera on a tripod or a sturdy spot, and let the exposure run for about 30 seconds. You may have to play with the settings, depending on the size of your aperture and the quality of light visible at your location. Good luck!
This article was updated from an earlier version to include new information about the zodiacal light’s origins.