The doppelgänger effect

Here’s a good one for the month that includes Halloween. Last May, my fiancee, Deborah Carter, and I were on Mauna Kea, Hawaii, just below the summit and its splash of telescopes. We stood on the shore of Lake Waiau in the rarified air at 13,000 feet (4,000 meters) altitude. The Sun was near setting, and as Deborah enjoyed a moment of solitude gazing into the lake, I sauntered off to take in the Mars-like terrain. On my return, Deborah looked perplexed, telling me of a weird phenomenon she observed.

“As I gazed into the lake, I felt a need to look behind me. At first I saw a dark line in the earth above my shadow and wondered what it was,” she later said. “I thought perhaps it was a fissure. So, I decided to walk over and see it, but when I moved, it also moved. I was overcome with a feeling of not being alone, that there was a ‘presence’ there, that I was being watched. I stopped in my tracks. All of this happened in a matter of seconds. Then I moved again and logic kicked in, and I thought that it was a second shadow but wondered how it was being made. Then the second shadow disappeared.”

Shadow people
After hearing Deborah’s account, I scanned the terrain and at first saw nothing out of the ordinary. Our shadows were long and thin, as you would expect from a low Sun. But I didn’t see a second shadow. When I walked away from a distant patch of rocks, however, I noticed a faint dark streak on the ground. It lay well above my shadow, and it followed me. When I raised my arm, so, too, did my shadow and the “streak.”

When Deborah saw this again, something clicked. She turned around and found the solution: The Sun shining over our shoulders was creating our normal shadows. And an image of the Sun reflecting off the lake’s surface allowed the second shadow to form.

Being lower than our bodies, the Sun’s dimmer reflection projected a new set of fainter shadows higher up onto the wall of the rocky depression we were in. Two Suns equaled two shadows. For a moment, I felt like I was standing on an alien world orbiting a binary star.

After giving the phenomenon some thought, I decided to call it the doppelgänger effect. The word comes from the German doppel (double) and gänger (walker or goer). It commonly describes someone who looks exactly like another person, but it also refers to an apparition in the shape of a person — as in the twin shadow we saw.

A “hollow” phenomenon
Just before sunset, I observed another curious phenomenon related to the first. Tall rocks and grasses in my normal shadow shone brightly through it, causing it to glow and look hollow. Deborah also saw this before the effect vanished once the Sun’s reflection disappeared.

This complementary effect is similar to fill-flash in photography — a technique that uses a flash to illuminate details hiding in the shadows of an otherwise bright image. In the case at Lake Waiau, the reflected Sun served as the flash. As soon as the image vanished, our single shadow no longer looked hollow.

As always, send what you see and think to sjomeara31@gmail.com.