Mirages

by Deb on March 7, 2011

Post image for Mirages

We spend a lot of time in the car, given where we live.  Not day to day, but every couple of months we do the long trip to the nearest town.  So we spend a lot of time trying to catch up to the puddles on the road.  We pick a landmark they are right next to, so we know, definitely that when we get to the tree there will be a lake.  But there isn’t.  And somehow the water manages to get around behind us so we’re surrounded, but we never find it.

These are mirages, called appropriately highway or desert mirages.

Basically, the air around the earth is like a giant prism or lens that light from the sun travels through.  Along the way the light is refracted or bent.  Sometimes when it bends it splits to form the blue sky, sunsets and sunrise, rainbows and moonbows.  Mirages are another example of this bending, but they form because different parts of the atmosphere are hotter or colder.  This makes them more or less dense, and means they bend light differently.

In the highway mirage, the bitumin of the road gets very hot and heats the air directly above it, forming a layer of hot air underneath a layer of cooler air.  It doesn’t need to be large, just a few centimetres or metres. When light goes from the cool air into the hot air it is bent and can go right around to reach your eyes travelling upward.  Of course your brain assumes the light has travelled in a straight line, so it must have come from the ground.  Since the main things we know of that reflect the sky are water bodies, that’s what your brain thinks it is.  The movement of the air as it warms and rises even makes it shimmer and move.

inferior mirage

A desert or highway mirage.

This is a type of inferior mirage, because the image appears below where the real object is.  Inferior mirages are also common when looking at the sun at sunset, they appear as a ‘rim’ below the sun.

Superior Mirages

A superior mirage is basically the opposite, when a layer of cold air is trapped under a layer of warm air.  The light rays are bent upwards and it appears as if the object is in the sky.  This is much less common than the inferior mirage because it’s unusual for air near the ground to be colder, so it occurs mainly in arctic and antarctic areas.

It can even show objects that are usually below the horizon, and is probably the explanation for the Flying Dutchman legend, a ghostly ship that sails through the sky. Depending on the position, size and temperature of the layers the mirage may be right way up or upside down as the light is bent differently.

Superior mirage

Superior mirage showing an inverted floating ship.

Fata Morgana

Fata Morgana is Italian for Morgan Le Fay, King Arthur’s fairy half-sister.  She could create castles in the air, which is exactly what Fata Morgana mirages look like.  They are a very complicated type of superior mirage, where several layers of air are interacting.  They have several images, with some inverted and others the right way up.  Because of the layers and movement of air they are generally very distorted and make it difficult to identify what is causing the image.

Fata Morgana

Several superimposed changing Fata Morgana of a boat. By Mila Zinkova (Click for a larger version)

Fata Morgana can occur in many places, especially deserts, and have been put forward as an explanation of the Australian Min Min lights and other UFOs.  A Fata Morgana of headlights or Venus can look like an extremely bright light that is moving erratically and quickly, vibrating or appearing to spin, changing colours as the light is split, and even disappearing suddenly.

I also happen to live just north of ‘Australia’s UFO Capital,’ Wycliffe Well and have had locals here tell me about the UFOs they’ve seen.  Being the skeptic that I am, I suspect it has more to do with the temperature and weather out here, than super-advanced aliens zooming about in (literally) the middle of nowhere.  Especially given the similarities between the descriptions of the UFOs and the descriptions of mirages.  But I think it’s just as fascinating.

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{ 1 comment… read it below or add one }

@downtogirth March 7, 2011 at 8:16 am

ScienceMum you have the most awesome blog – I always learn something new THANK YOU!! xD

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