Cameras can be strange machines. We tend to think of cameras as devices that faithfully record the nature of the landscape around us, which they do…at least most of the time. When this paradigm does break down, it is usually because the camera has failed to record something important, something that made a moment or an experience worth remembering. Oftentimes when this happens, we become disappointed. How many times have you been scrolling through vacation photos and lamented at how poorly they turned out? Sometimes we even realize the limitations of the camera in the moment itself. Perhaps you’ve experienced something akin to standing on the rim of the Grand Canyon at sunset and becoming so resigned to the fact that no photograph will ever satisfactorily capture the grandeur in front of you that you begin to ponder the option of chucking your camera into the great chasm below.
On rare occasions though, the camera delights us by managing to capture even MORE than meets the eye. After returning from a recent camping trip to the San Juan Islands in northwest Washington, I was surprised to find an unexpected apparition in some of the long-exposure photographs I took from our campsite on the west coast of San Juan Island.
Getting to the San Juans is no easy task; it took me about 5 hours to get there, even though “there” is just 35 miles by air from my front doorstep. As a result, the islands can feel remote and isolated, but standing along the coast at night is a not so gentle reminder that you’re actually only about eight miles across the Haro Strait from Victoria, a metro area of more than 300,000 people. Taking advantage of a somewhat rare, perfectly clear Pacific Northwest evening, I took a series of 15 second exposures looking west across the strait which I composted into this 180 degree panorama:
The first thing you notice is the egregious light pollution from Victoria. Even the skyglow from Vancouver, five times further away but seven times more populous, is visible through the tress. Amongst all of the artificial light sources though, some natural ones still manage to shine through. The faint tendrils of the winter Milky Way just barely register on the camera’s sensor but the bright winter constellations of Orion, Canis Major, and Taurus forcefully punch their way through. If you look really closely, you’ll see a faint, slightly elongated, pale blue glow hiding in-between the lights of Victoria and Sidney. This is a phenomenon known as the zodiacal light, and it’s what took me by surprise when I started putting these images together. Here’s an annotated version to help you out:
See it? It’s a slightly different color than the light domes and isn’t as round and symmetrical as the light radiating from the cities, but rather looks squished and creeps upward into the sky at an angle. What really betrays the nature of this mysterious glow is its location: it coincides almost perfectly with the ecliptic, the plane of our solar system which is also the apparent path that the Sun, Moon, and planets follow as they move across the night sky.
What does this have to do with the zodiacal light? Well, it turns out that the plane of our solar system is home to lots and lots of dust. Not the dust made of dead skin cells and carpet fuzz you find around your house, but rather interplanetary dust particles made mostly of carbon, silicon, and oxygen. These dust particles are really small, on the order of 10 micrometers in diameter, about the size of a mold spore. The exact source of this dust is controversial; most of it is thought to be the result of collisions between comets and asteroids although some may be leftover from the formation of the solar system itself, tiny pieces of debris that never got incorporated into a planet. Regardless of where it cam from, the dust is really good at reflecting sunlight. Just after sunset (or just prior to sunrise), the angle between the Sun, dust, and Earth is such that the light reflected of the surfaces of the innumerable dust particles reaches our eyes (or cameras) here on Earth, giving rise to the zodiacal light.
When you consider how small the dust is (and that the dust particles are on average more than 2 miles apart from one another!), it’s not hard to understand why the zodiacal light is so faint and difficult to spot. Due to a quirk of celestial geometry, spring is a great time to observe it from the northern hemisphere, but even then spotting it with the naked eye requires extremely dark skies. The conditions in the San Juans, while darker than many spots in Western Washington, are far too light polluted. However, digital cameras are MUCH more sensitive to faint sources of light than the human eye. It’s actually rather common for a camera to detect things in the night sky that aren’t visible otherwise. On the night I saw the aurora borealis for the first time about a year and a half ago, its presence was first betrayed to me as a faint green glow hugging the horizon on my camera’s LCD screen, hours before it became bright enough to see with the naked eye. If not for my camera’s ability to detect it, I would have been fast asleep instead of standing in a marshy field near the Canadian border when the aurora dramatically brightened a few hours later and streamers began appearing all over the sky.
Have you ever captured anything on camera that you found surprising? Share your thoughts or stories in the comments below.
I’ve been an astronomy nut ever since my parents gave me a small reflecting telescope for my 10th birthday. I located Saturn, complete with its too-good-to-be-true rings, within 10 minutes of setting it up for the first time, although my parents refused to believe me until they had a look for themselves. I majored in astronomy, own a telescope that barely fits in my car, and come to think of it, every “real” job I’ve ever had has involved astronomy. NASA’s Astronomy Picture of the Day has been my homepage for longer than I can remember.
Given my disposition towards both astronomy and photography, it seems superfluous to say that I’ve always enjoyed astrophotography. Taking photographs of celestial objects presents a set of challenges not encountered by photographers who go home after the sun dips below the horizon, the majority of which revolve around the fact that most astronomical objects are rather dim, requiring long exposure times and extra equipment to capture.
Quite frequently I’ll get asked if I’ve ever seen any UFOs while gazing up at the sky. My standard response is that, while I’ve certainly seen a lot of weird *#&@ in the sky, I’ve yet to see anything that didn’t ultimately have a logical explanation, even if it took a little head-scratching to figure it out (high altitude weather balloons are the worst!).
A prime example of this occurred this past summer during a nighttime observing and photography session. I was attempting to get a 180 degree panorama of our home galaxy, the Milky Way, stretching across the summer night sky. I had my camera mounted on a tripod head that compensates for the rotation of the Earth, allowing me to take exposures several minutes in length while avoiding star trails in my images. It was dark and clear enough that I was able to get some good shots of the summer Milky Way and its complex and sinuous inky-black interstellar dust lanes, as well as some decent shots of some galaxies and nebulae through a telescope:
The Milky Way in the constellations of Scorpius and Sagittarius. This portion of the Milky Way is home to the nucleus of our galaxy, making the Milky Way appear brighter here than anywhere else in the sky.
The Lagoon Nebula, also known as M8, a vast cloud of hydrogen gas giving birth to new stars. A “stellar nursery” as astronomers like to say.
While my shots of the galactic center in the southern sky were turning out well, as I began to pan my camera around to the east and then finally north, I noticed that faint but noticeable bands of diffuse red and green light were creeping into my image.
My immediate thought was sensor noise. The CCD chip on my old DSLR (a Nikon D70) had a habit of heating up during repeated long-exposures. This thermal radiation from the sensor manifested itself as a bright purple/pink haze occupying one corner of the photo, making any attempt at serious astrophotography futile. Perhaps something similar was happening here. I quickly ruled this out for a number of reasons. Most importantly, the apparition was showing itself only in photos taken towards the north, meaning that the source couldn’t be the camera, but rather something in the sky itself. The colors ruled out high clouds, and it wasn’t in the proper direction to be the result of artificial light pollution. The closest city of any significant size to the northeast was several hundred miles away.
Whatever it was, neither myself or any of my observing companions could see it with the naked eye. A bit eerie perhaps, but not at all uncommon. Many astronomical phenomenon are too faint to see without long-exposure photographs. In fact, the first time I saw the aurora borealis, I captured it with my camera several hours before it became bright enough to see with the naked eye.
A auroral display was actually my second thought. What I was seeing in my photos definitely resembled one. Red and green are the colors produced by nitrogen and oxygen, the two primary components of our atmosphere, after being excited by collisions with magnetic particles brought to Earth by the solar wind. Most auroral displays consist of some combination of these two colors and what I was photographing appeared only in the northern sky which fit the theory to a tee. Furthermore, the Sun had been especially active in the week or so prior. It was perfect except for one slight problem: I was in Colorado.
Auroras in Colorado are definitely not unheard of….but not exactly common either. One thing was certain: if an aurora HAD crept this far south, then the northern portions of the country would simultaneously be getting the show of a lifetime. A quick check of spaceweather.com, the one stop shop for up-to-the minute aurora information, showed this was not the case. Strike two.
I actually didn’t figure this one out until many days later, when I inadvertently ran across an article about some Pacific Northwest photographers who had captured something called “airglow” in some photos of the Milky Way taken at Mt. Rainier around the same time. A momentary glance at their photos and I knew I had my answer.
Here’s the final panorama I produced. The airglow (red and green splotches at left) was changing rapidly enough that it caused major headaches trying to stitch the images together. Consequently I didn’t quite get my 180 degree panorama, there’s a bit missing on the northern end (lower left).
Airglow is exactly what it sounds like (a rare thing in science, I know…): glowing air. Incoming solar radiation and cosmic rays ionize oxygen and nitrogen atoms in our atmosphere during the day and then then these atoms regain their electrons at night, emitting light in the process. This is similar to what happens during an aurora, except that it’s happening ALL THE TIME. Airglow is always there, it’s just really, really faint; you need to be somewhere extremely dark to have a chance of seeing it, even with a camera. Even a miniscule amount of light pollution will render it invisible. It does tend to be brighter when solar activity is high, although it is not nearly as dependent on the solar cycle as its brighter cousin, the aurora.
So what began as an unidentified and undesirable annoyance in my photos (and when trying to stitch together my panorama, boy it sure was!) turned out to be a rarely captured celestial phenomenon I had never even heard of, much less one that I had intended on photographing that evening. Next time someone asks me about UFOs, I’ll just refer them to this page.
Some photos from a week exploring southern Utah, Bryce Canyon, and the Grand Staircase: