Yep, you read that right – mirages don’t just happen in deserts. While on holiday in the Bay of Fundy we noticed that a distant island (Isle Haute) looked really strange through our camera. The island seemed to have straight vertical walls and was “cut” by a band running across it:
If we zoom into the island a bit more, you can see things more clearly:
Cosmoboy was instantly intrigued and figured that it had to be an atmospheric effect.
But it couldn’t be like a mirage in a desert, since those mirages bend light that is heading toward the ground back up toward you, the viewer. From your perspective you see the blue light of the atmosphere coming from right at the ground.
You’re actually more familiar with the same thing happening when you drive along a road on a hot day, you can see wavy bluish spots ahead of you on the road, like in this picture:
The process is exactly the same though. It’s all caused by the layer of air next to the ground (or road) getting really hot. The change in temperature leads to a change in the way light is bent by the air. If we draw out the path of light it looks something like this:
This type of mirage is called inferior because the light appears to be coming from a place that is lower than reality.
OK, that still hasn’t explained what was going on the other evening. We weren’t seeing the sky imposed on the sea, in fact it was probably the other way around. And that’s the key! We were seeing a temperature inversion, the air above the sea was colder than the air higher up in the atmosphere. It’s really kind of the reverse effect to what happens with an inferior mirage and is called a superior mirage:
The layer of cooler air tends to trap the light from a small area above the horizon into a narrow band – called at atmospheric duct. If you look in the photos you can see the edge of the duct really clearly! These ducts can direct light along the curvature of the Earth just like an optical fibre, check out the story of the ship marooned at Novaya Zemlya.
If the mixing of temperature layers gets really complex then you can get some truly weird shapes occurring. Just a few seconds later this is how things looked:
If the shapes change and dance in front of your eyes then the effect is called a “Fata Morgana”. The name is actually Italian for “Morgan le Fay” the sorceress of the King Arthur legend. She is also associated with sirens, which ties her to the island of Sicily – a region known to have these optical phenomena on a frequent basis.
There’s also good reason to believe this phenomenon is responsible for some UFOs identified by RADARs.
Fundy – it’s more than just about the tides! 🙂