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Posts Tagged ‘obelisk’

What do you do to cope on a hot sunny day? Most of us stay indoors in an air-conditioned space, possibly with a cold beverage. Dragonflies do not have those options, so many of them assume a pose, often known as the obelisk posture, in an attempt to regulate their temperature by reducing exposure to the direct sunlight.

You may seen dragonflies in a handstand-like pose, looking like gymnasts in training—that is the obelisk posture. The dragonfly lifts its abdomen until its tip points to the sun, thereby minimizing the amount of surface area exposed to solar radiation. At noontime, the vertical position of the dragonfly’s body suggest an obelisk, which in my area immediately brings to mind the Washington Monument. According to Wikipedia, scientists have tested this phenomenon in a laboratory by heating Blue Dasher dragonflies with a lamp, which caused them to raise their abdomens and has been shown to be effective in stopping or slowly the rise in their body temperature.

While visiting Green Spring Gardens last week on a hot humid day, I observed obelisking behavior in a male Blue Dasher (Pachydiplax longipennis) and a male Eastern Amberwing (Perithemis tenera). I have always been intrigued by this pose and would love to try it out to see if it works for thermoregulation in humans too. Alas, I lack both the upper-body strength and the lower body flexibility to make a go of it, so I’ll continue to be merely a spectator of these beautiful little acrobats.

Blue Dasher

Eastern Amberwing

© Michael Q. Powell. All rights reserved.

 

 

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When you are staying in the center of Paris and walking almost everywhere, you don’t really need to plan to see cool things—they surround you all of the time. Late yesterday afternoon, as the sun was getting low on the horizon, I had to cross the Place de la Concorde to head towards home and captured this shot of the Luxor Obelisk in the center of the square.

As I was doing a little research on the obelisk, mostly relying on Wikipedia, I learned that it is a granite column, 75 feet (23 meters) high, including the base, and weighs over 276 tons (250 metric tons). Even today, transporting and erecting something this big would be an engineering challenge. Imagine what it was like trying to do so in 1833.

For some reason I thought the obelisk had been stolen, but the Archaeology Travel website provides the following details of the transaction.

“Initially both the obelisks from the Luxor Temple were promised to England. Following diplomatic negotiations they were both gifted to France by Pasha Muhammed Ali. In return,  King Louis Philippe gave the Pasha a large clock. The clock is still in place in the clock tower of the mosque at the summit of the Citadel of Cairo.”

The Wikipedia article referenced above wryly notes that after the obelisk had left Egypt, the large mechanical clock provided in exchange turned out to be faulty, probably because of damage during transport.  “The worthless clock still exists to this day in a clocktower in Egypt, and is still not working.”

Place de la Concorde

© Michael Q. Powell. All rights reserved.

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Male Blue Dasher dragonflies (Pachydiplax longipennis) assume this handstand-like position, called the obelisk posture, when they feel threatened or want to minimize exposure to the sun. I was leaning a little closer than normal to this dragonfly, because I had a 100mm lens attached to the camera and not a longer zoom lens, so maybe that caused him to be a little alarmed. As the weather warms up and more dragonflies appear, I am sure that I will be getting a lot more shots of Blue Dashers, which were my favorite dragonflies to photograph last summer.

dasher1a_blog

© Michael Q. Powell. All rights reserved

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