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Hey, I learned about this in grade 8 physics! And then forgot. Some 20 years ago I remembered about it when I was reading an article on measuring the distance to the Moon with a laser. And then forgot.
It started last O
ctober when I looked up from my office desk and was surprised to see the Manulife building reflecting a rising Sun that was south of east - I knew that the nearly north-south oriented windows could not bounce the sunlight to me at that time of year, it only works on the summer (northern) side of the equinox - it's basic geometry.
If the Sun is rising to the southeast somewhere behind me, its reflection is off somewhere to the northeast.
But I know that the Manulife building also has angled windows:
so it must be those facets! I calculated what their angle must be in order to reflect the Sun that morning (I knew its azimuth thanks to planetarium software). Then for each of our 20-ish viewing locations around the city (e.g. Riverside Drive, Strathearn Crescent), I proceeded to calculate where the Sun had to be for those Manulife facets to reflect it my way.
I didn't think anything more of it until I was taking a closer look at the angles of the south facing windows of various buildings over the holidays. Eventually I came across the Canadian Western Bank, and took a closer look at it from above using Google maps (I've highlighted in black the angled facets):
The memories of grade 8 physics and lunar ranging hit me: corners! Mirrors set at 90 degrees to each other have a special property of reflecting light right back to the source, no matter the angle. From bikexprt.com:
The Apollo astronauts placed corner reflectors on the Moon:
What the picture doesn't show is that the reflector actually uses an array of open-faced cubes, to handle variations in the vertical angle. Whatever the orientation of the Moon (libration) or position of the observatory firing a laser at it, the light comes right back! From the time delay the Moon's distance can be calculated.
Back to Earth and my skyscraper corner reflectors. As long as the Sun is right behind me, I will see its reflection from the building in front of me! Sure enough, when I ran the numbers, the Sun, me, and the building were in a straight line. Geometry works. It was only a matter of time to run the numbers for each site to make a list of the azimuth that the Sun (or Moon!) has to be to give me a reflection from the corners.
On the morning of February 7th, I drove out to Meridian Street (just north of Our Lady Peace cemetery at the southeast corner of the Whitemud and Henday) and was treated to a sparkling view.
As a bonus, I witnessed a bunch of unexpected reflections from buildings that did not have corners and were angled "wrong". But then I quickly realized that for corners to work, the faces don't actually have to be connected:
Now the fun and games ramp up for us to corner capture a Moon!
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