At our last Photowalk, we got to the Great Salt Lake almost 3 hours before sunset, which gave us some time to kill. We did so profitably, but it made for a long session by the time the light got really sweet. With the right tools, it’s possible to consistently predict the cascade of sunset; we can calculate backwards to know just when to be on location. (That’s one great thing about our Photowalking adventures – there’s always something we will do better next time, but everyone has fun regardless.)
In December 2006, I photographed a spectacular instance of the atmospheric phenomen known as the Belt of Venus, the glowing pink color on the horizon in the opposite direction to the sun. The earth’s shadow is the blue band below the pink layer. It showed up the day before in the same location, but the winds were gusting at 40 mph and I couldn’t get a sharp image. Perhaps a proper meteorologist could describe the conditions that set it up (I’m guessing particulates or moisture in the air). I’m no weatherwoman, but I do know what time to look for it. I print out a custom sunrise/sunset calendar before any photography trip, and here’s how.
I use the www.sunrisesunset.com custom calendar menu–the places I photograph usually aren’t on the site’s default pages. I check every box in the menu because I use the twilight times to figure out when to reach my location. The website gives formal definitions for each phase of twilight; it doesn’t take long for a photographer’s eye to calibrate the scientific descriptions to what we actually see in the field. At sunrise, astronomical twilight is when the sky just begins to lighten in the east, barely perceptible, but critical if you are doing star-trail photography. By nautical twilight (originally defined as when a ship’s mast could be detected on the horizon), things are starting to get quite bright in the eastern sky. You can turn the car lights off at civil twilight, but for dawn landscape photography, that’s when sunrises start to get interesting, way to late to be driving to location.
When I don’t have to drive or hike too far to my (previously scouted) location, I get up at astronomical twilight, get my location by nautical twilight, and am ready to make a picture by the start of civil twilight.
The EXIF data says this image was made at 7:01:30, facing to the west, away from the rising sun. The camera clock isn’t perfectly accurate, and San Xavier del Bac is some distance from Tucson, but the numbers are close enough for generalization. The Belt of Venus, if visible, will be strongest in the last few minutes before sunrise. The earth is turning toward the east, the sun is lighting the atmosphere in the pink belt, and the red light is scattering to make the pink color. In the next few minutes, the earth shadow will drop lower and disappear, and then the pink will lower and fade out. If there were clouds in the western sky, they would be lit up – here we are actually seeing the air itself.
Long before the Belt of Venus hits the western horizon, the eastern sky has potential to color up, depending on the cloud cover. Color will be sweeping from east to west as the earth turns our location toward the sun. (In Choteau last week, I saw a faint Belt of Venus almost directly overhead, long before it was in an interesting position relative to the mountains to photograph; I entertained myself in the cold by watching it drop down to the horizon.) Usually, the pink band is overwhelmed by the first rays of the sun. Once the sun fully clears the horizon, there’s typically a golden few minutes to hour of sweet light. Then it’s time for breakfast
For sunset, the pattern reverses, but the sequence is just as predictable. The Belt of Venus may appear again; in the mountains, we call it alpenglow. To use the twilight times for planning an evening shoot, I would want to be on location about 90 minutes before sunset, and plan on staying well past civil twilight. In northern latitudes in summer, hitting dawn and dusk can make for some long days, which is why I’m trying to learn the essential skill of napping.
One way to practice with the calendar data is to simply print out the current chart for your location, and make some observations even if you can’t get to a brilliant sunrise/sunset location. The experience will pay off the next time you are in the field, well-timed to make that amazing photo.
ETA 2014.12.28: updated links and note that they now have an IPhone app!