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Newsletter

August, 2010

Mirages: The Result of the Heat – and Cold – of August

In the northern hemisphere, August reigns as one of the hottest months. Mirages and heat waves are common, often appearing as shimmering puddles of water on roadways, parking lots, and desert vistas. In the past, mirages were sometimes thought to be tricks of the eyes or even hallucinations, but in actuality they are neither: the images seen are real, and can be photographed. When photographed, mirages are usually meant to convey the concept of sweltering heat. However, they can also be used to add a wide range of completely natural artistic elements to an image that leave the viewer questioning whether the photograph has been seriously manipulated, despite the fact that it has not.

Mirages are especially common in areas containing large amounts of sand or asphalt. This is because these two substances absorb large amounts of heat from sunlight, which in turn causes the air directly above them to be significantly hotter than the air further away. As light passes from the denser, cooler air above into the warmer, thinner air next to the superheated sand or asphalt, the light gets refracted, or bent, in an upwards curve, causing what is known as an inferior mirage. It is called “inferior” not because it is of a lesser quality than any other kind of mirage, but because the image in the mirage appears below the actual item being seen. It is as if we are looking down into a bowl, and can see on the inner curve of the bowl what is actually atop the opposite rim. This is why lakes and water are often imagined to be seen: the blue sky is being seen below where it should be, causing it to appear as a body of water on the ground. It often shimmers, too: inferior mirages are unstable, because hot air rises and cool air sinks. As the two air masses mix, they cause turbulence, distorting the light waves even more. This causes the apparent pool of water to shimmer, and the characteristic waviness of the horizon, as illustrated by our featured picture this month, Watercolor Rhinoceros.

However, mirages do not only occur in hot weather. They also occur in areas where the temperature conditions are reversed, namely a layer of significantly colder air next to the ground, with a warmer layer above. These mirages are, not surprisingly, most commonly found in the polar regions. (Let’s not forget that August in Antarctica is in the middle of winter!) In these instances, the light rays are refracted downward – as if our bowl were flipped upside down. The item being seen is still on the rim of the bowl, and we are still seeing it on the bowl’s curve, but because the bowl is now upside down, the mirage now appears above the actual item. These types of mirages are called superior mirages because of their location above the object being seen. This can result in items appearing to float above the horizon. An especially interesting aspect of superior mirages is due to the curvature of the earth: some of these mirages can even result in being able to see things that are still below the horizon. Imagine taking our upside down bowl and putting it on the edge of a table, such that the rim where our object is located is now below the table’s edge, but the curve where we see the mirage is still above. The table edge represents the horizon line; our object on the bowl’s rim is now below the horizon, yet we can still see it on the curved surface of the bowl. How cool is that? (Pun only partially intended…)

Throughout the ages of sea exploration, superior mirages were responsible for a good bit of confusion as to the possible existence of islands, ships, and other objects. The mirages are often hazy and distorted in appearance, and may have led to the legends of ghost ships. A particular type of superior mirage called a Fata Morgana, for example, is considered the likely origin of the legend of the Flying Dutchman (as well as many modern-day UFO sightings). Some early polar explorers reported seeing mountains in the sky and flying ships, and even Robert Peary, famed Arctic explorer and the man credited with being the first person to reach the North Pole, named a land mass which he believed he saw in the far distance Crocker Land -- a land mass that later proved to not exist, and which is now widely believed to have been a Fata Morgana mirage. A later search for Crocker Land cost one man his life and stranded the remaining crew for four years.

Score: Mirage 1, Explorers 0

August’s Fun Facts

Since we’re all suffering through the heat (or cold) that August brings, this month we thought we’d put this sweltering / frigid day in perspective:

The highest temperature ever recorded was in Al ‘Aziziyah, Libya, on September 13, 1922: 136.0 F (57.8 C)

The lowest temperature ever recorded was at Vostok Station in Antarctica on July 21, 1983: -128.6 F (-89.2 C)