Twilight Wedge from Sunlight Peak

Twilight Wedge from Sunlight Peak, Weminuche Wilderness, Colorado

Worried that I might not have made the best possible image during my first shoot on Sunlight, I decided to try again the next day. This time I found the easiest way, even in the dark, since I had seen it in daylight just 24 hours earlier, and reached the summit about 45 minutes before sunrise.


One of the privileges of shooting sunrise from the summit of a Fourteener is the opportunity to witness amazing displays of natural light. To understand how a normally blue sky can turn pink at sunrise, you need a quick primer on atmospheric optics. Light as it leaves the sun is composed of all wavelengths. When it strikes the Earth's atmosphere, air molecules begin to scatter the light in a process called Rayleigh scattering. The amount of scattering is inversely proportional to the wavelength. Blue light, which has a short wavelength, scatters much more than red light, which has a longer wavelength. On a clear day, the sky is blue because we see blue light scattered to our eyes from the air molecules in the path of our gaze. At midday, we see the color of the sunlight that passes directly through the atmosphere and illuminates objects on the ground below as white.


The length of the path sunlight takes through the atmosphere at sunset is much longer than at midday. That gives air molecules many more opportunities to scatter the blue light out of the beam of sunlight, leaving behind only the warm red and orange hues, which pass straight through. If some clouds are present on an otherwise clear evening, this direct, warm-toned sunlight turns the clouds to gold.


That same selective sorting of wavelengths via Rayleigh scattering causes the pink band of light seen in this image, looking west from the summit of Sunlight toward Mt. Eolus, North Eolus, Turret, Pigeon and Monitor peaks. Light from the rising sun, which is just below the horizon, takes a very long path through the atmosphere from east to west, losing most of its blue light as it goes, then bounces off air molecules and dust particles in the western sky and returns to your eye as a luminous pink glow. The effect is most pronounced at high altitude when your horizon is at the same elevation as you are, or even lower ‒ a description which exactly fits the summit of a Fourteener. The blue band of sky visible below the pink band is actually the Earth's shadow. The blue band is thickest at a point on the western horizon that is directly opposite the sun. The thickness of the band tapers off as you look either north or south of the "anti-solar" point, which gives this beautiful phenomenon its name: the twilight wedge.


Just to keep the record straight: I did not set up my 4x5 field camera on the frighteningly small and extremely exposed true summit of Sunlight but rather on the rocky terraces about 15 feet lower. Perhaps the 20 years that had passed since my hard-core rock-climbing days had reawakened my "instincts of self-preservation," as my father would have put it. In fact, I didn't even stand up on the summit, a feat said by some to be a rite of passage for "real" mountaineers. Instead, I sat there, soaking in the amazing view and wondering what could possibly have possessed Carl Blaurock, who is said to have performed a headstand on the exact summit during a CMC outing in 1920!

Glenn Randall Photography

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