A Quadruple Reflection

by Alister Ling June 2017 Stardust

The day the camera died, worlds aligned, light took an extended journey: the expected and the unexpected.

The nearly full Moon shone through a gap in the clouds above the city at dawn on May 10th, 2017. The orange rays of the Sun had yet to flood across the Beaver Hills to brilliantly illuminate the skyscrapers of Edmonton. Through all the noise of the traffic, I suddenly noticed the absence of the now familiar burst of "click---ah--clicka-ah-clicka-click-click-clika" of my camera taking 6 exposures back-to-back needed to capture the high dynamic range of the scene. Dang, my second corrupted SD card! This time I was prepared; I swapped it out for another, restarted, and 6 frames later nothing. Popped the battery and card out, waited a few seconds, put them back in, and the camera boots up. Phew. Click-dead. Again. Again. Okay, Zen-mode: we're going to just watch.

Twelve hours later, I joined Luca on the opposite side of town, on the side of 156St overpass to the Yellowhead to watch the Moon rise behind our city bathed in the light of the setting Sun. The west was nicely clear but the southeast had 2 degrees of cloud along the horizon. This was not unexpected since we were humming and hawing about trying for the event. But I had not seen Epcor's corner reflectors in action. That was to be expected: when a pair of windows (in this case two columns of windows) come together at 90 degrees, they reflect back light from the very direction it originated (this property is used for bicycle reflectors and lunar ranging). The Sun was directly behind us lighting up Epcor right on time. Sadly for me, my camera did not work with recharged batteries and yet another SD card, it simply died on a shutter press, and after a couple of iterations, did not even boot up.

Image by Luca Vanzella ©2017

All that was left was for the Moon to rise, but bit by bit, the building low in front of the Bell and the copper Scotia Bank put out some deep orange and red! I knew the Scotia was oriented at the wrong angle, so it had to be a secondary reflection off another building, the separated pair nonetheless acting like a corner. The Moon crested the clouds, Luca finished up and we headed back home.

There's nothing like a shot of dopamine from successful puzzle-solving to help console me over the loss of the camera, so I set myself to a bit of geometry and sleuthing. Out comes Google maps satellite view, my position angle/building angle formula, and a calculator (don't want to work unnecessarily hard, do I?). There was no building to pair as a corner with Scotia! The closest was IPL, but Scotia Bank is 6 degrees off of north (you can see its face is not parallel to the street) and IPL at the bottom is 0, so it doesn't work. Double check the math, follow the light ray, backwards from us, angle of incidence equals angle of reflection... hang on, Enbridge Place would catch the rays from IPL, pass them onto the Manulife, and back to us! That explains why the glints from Scotia were not as bright as I would expect from a secondary reflection.

North is to the upper right.

Now in case there is a descendant of Euclid reading this (or someone very comfortable with angles) who says "Hang on, three of those buildings are almost exactly 90 or 180 degrees from each other, and you said that Scotia Bank was 6 degrees off - it doesn't add up to a multiple of 180 and the in-out lines on your diagram are parallel !" Indeed, the rays should not be drawn parallel, I made a mistake in my enthusiasm of wanting to share my discovery with Luca. Sun-us-Epcor is a straight 180, but Sun-us-Scotia Bank is actually 174. From our vantage point, the angular separation of Epcor to Scotia is 6 degrees, which, of course, is the exact offset that Scotia's orientation throws into the angle calculation. If it wasn't, we would not have seen the event. Phew, we don't need to invoke warped space!

Epilogue: My camera has been returned to me ready to go for another half million frames.