This is not a title of a psychedelic song from the sixties with no diamonds.
In fact it refers to an event that happened in the late eighteen-hundreds.
On Thursday August 16 in the year of 1894 some folks in Buffalo who were awake that morning saw something spectacular. They saw an entire city floating in the sky. Toronto unlike today was some puritan boring place at the time: pretty much no one knew about its existence outside of Canada. But some buffalonians recognized some of the well-known churches and other notable landmarks and some must have exclaimed: “holy cow, they finally moved Toronto into the sky.” Toronto is still alive and kicking today, thank you very much.
Here is a hand-drawn depiction. Too bad no one took a photograph of the event:
This is how it was described in a Scientific American article published on August 25, 1894:
The phenomenon is called a Mirage or more fancifully a Fata Morgana. Mirage brings to mind Austrian magicians with white tigers in Vegas or Palm trees in the desert. But this event did not happen in the desert.
How did this event happen in Buffalo more than a century ago? Explanations like mass hallucination or space alien invasions come to mind. But it can be explained rationally using simple optics.
Firstly let’s look at a map that shows where Toronto is located relative to Buffalo.
Lake Ontario and Niagara Falls separate these two cities. The Falls are famous and popular with newlywed honeymooners. More seriously, let us focus on the huge body of water left carved out by the retreats of the glaciers after the last ice age. The mix of cold water and a hot summer day with no winds and disturbances are the key to understanding this event.
Light rays do not always travel in straight lines. Anyone who has to wear glasses or contact lenses knows this. Our vision is sometimes blurred and lenses bend incoming light to focus it on the back of our retinas. Our brains are now happy with a cleaner input.
Let’s go back to the Buffalonians on that morning. On that day the difference in temperature between the lake and the air created a gigantic lens. In this case the lake is cold and the air is hot. And rays as it turns out like to travel the path of least resistance. That is a basic principle in physics. Light rays like to live in less dense air.
So this is what happens:
In a nutshell a Buffalonian thinks he is seeing Toronto in the sky because when he is looking into the sky he is actually seeing what is on the ground. I hope the following depiction makes it crystal clear.
That explains the illusion: just cold water and hot air.
I wrote a paper on this back in 1996 when I was living in Paris. You can find the paper here:
The research emanated from the problem of modeling the shimmering above a fire. After I published a paper on fire at SIGGRAPH many people asked me to model this phenomenon. So I did some research, wrote some code and then wrote a paper: and voilà.
Next I might write about how our perception is an illusion of the real world.
I gave a related talk about that here:
What about the "flying dutchman?". This is another fata morgana off the coast of South Africa: