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When returning from our holidays this past year my daughter took the photo bellow. In it you can see the shadow of our plane upon a cloud surrounded by a radial rainbow. This optical phenomenon is called the “Brocken Spectre”. It occurs when the shadow of a person or an object is projected on mist or clouds. The shadow is often accompanied by a multicolored halo called a “Glory”, which is created when the light from the sun on the periphery of the shadow is diffracted by water droplets in the air.  Airplane Brocken Spectre The illusion is named after Brocken Mountain, which is the tallest mountain in the Harz Mountain Range in Germany. The foggy weather in this mountain range has led to many instances of locals witnessing and describing the Brocken Spectre throughout history, which has created a lore of fantastic tales associated with witches and devil worship. The first recorded description of the Brocken Spectre was made by the German theologician and natural scientist, Johann Silberschlag, in 1780.  Person Brocken Spectre The Brocken Spectre has been reported in many places throughout the world as well as by aviators since the early days of flying. It has been mentioned in works of literature by several authors including Charles Dickens and Lewis Carroll. Image of the airplane Brocken Spectre belongs to the author and can only be used with permission. Image of the person Brocken Spectre by Walter Baxter is used here under an Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0) license. For most people, clouds are these fluffy white things floating up in the air, which may give the impression that clouds are light, but nothing could be further from the truth. Clouds are created when water vapor condenses into minute water droplets due to changes in pressure and temperature, and water has weight. Those large cumulus clouds that you see up in the sky actually weigh hundreds of tons! The reason why clouds don’t fall is due to in part the same reason why ships built out of steel don’t sink. The density of the clouds is lower than the density of the underlying air. In other words, a given volume of air below the cloud is heavier than the same volume of air in the cloud, thus the cloud floats on this air. In cumulus clouds, this happens because as the warm air rises from the land it expands and becomes less dense. Additionally, the water droplets that make up most clouds are microscopic, and the effect of gravity on them is negligible and easily counteracted by the updraft currents within the clouds.  Kennett Square, Pennsylvania, is the site of Longwood Gardens, a world-class horticultural display garden with a wide variety of plants and trees of both beauty and interest. The garden is the brainchild of its founder, industrialist and financier Pierre DuPont, who began constructing it in 1906. Longwood Gardens features many native and exotic plants both abundant and endangered. But one of the greatest attractions of this site is its water, light, and music show in the Main Fountain Garden. This water display features more than 1,700 jets of water that are programed to move to music. Some of the jets can hurl water up to 175 feet up in the air. The average show, which lasts about 12 minutes, involves recirculating more than 10,000 gallons of water per minute. In the video below you can see a portion of one of the shows during the day. At night, the jets of water are illuminated by LED lights creating a stunning display of color. An additional feature of the show is the fire fountains. These are water fountains that have a fire burning at the top. This effect is achieved by injecting a stream of propane gas into the water jet and igniting it. In the video below you can see the fire fountains during part of one of the shows at night. Many plants have coevolved with other organisms (pollinators) to such an extent that the main or only means the plant has of transporting the male elements (pollen) to the female element (ovule) to assure reproduction is through the intersession of the pollinator. And the same time, many pollinators have become dependent on the nectar and pollen produced by plants for their nutrition. It has been calculated that without pollinators a third of flowering plants would produce no seed and half of all flowering plants would have their fertility reduced by 80%. Pollinators are estimated to contribute 24 billion dollars each year to the US economy by making possible the reproduction of plants of economic importance. The phenomenon of pollination is an active area of research in disciplines such as ecology and evolutionary biology. In the video bellow an Eastern Tiger Swallowtail butterfly (Papilio glaucus) feasts on the nectar of the flower of a thistle plant promoting its reproduction in the process. A wild plant took root in our garden. We decided to let it grow to see what it was. It turned out to be a Late-flowering Boneset Plant (Eupatorium serotinum), also known as Late-flowering Thoroughwort or just Late Boneset.  We immediately noticed that the plant was very fragrant and attracted quite a large number of pollinators. Below you can see a sampling of some of the pollinators that visited the plant. It seemed that all these pollinators were having a good time feasting on the nectar of our boneset plant and contributing to its reproduction. However, we then spotted a large bug feeding on a bee it had just caught. We were surprised at the structure with spokes in the back of the insect. What was this bug?  The bug turned out to a specimen of Arilus cristatus, the North American Wheel Bug. It is presumably called this because the spoke-laden structure in their backs reminds people of a wheel. The wheel bug is a type of the so-called assassin bugs which belong to the family Reduviidae. These bugs stab their prey with their very sharp proboscis and injects them with enzymes that dissolve the interior of their bodies, which they then proceed to drain.  But the wheel bug was not the only assassin lying in wait on our boneset plant. We also spotted a praying mantis lurking among the stems and leaves.  The mantis spotted a bee and moved with lightning speed upon the hapless insect, which became its meal.   So it seemed that our boneset plant could also be a death trap for some of our pollinators. The wheel bug and the mantis are both ambush predators. They frequent scented plants that attract their prey and lie in wait for the right time to attack. The drama of life and death in nature often unfolds right before our eyes, but we don’t notice it. And all it took was a fragrant plant in my garden to bring this reality to my attention. All photographs belong to the author and can only be used with permission. In the field of optics, a caustic is a set of rays of light that have been reflected or refracted by a curved surface and focused into another surface. The classic example of caustics or a network of caustics is the bands of light you get at the bottom of a pool when the light shines from above. The top of the waves crisscrossing the pool act like a convex lens concentrating light on a focal point. This is incidentally why they are called “caustics”, from the Greek “to burn”, as when sunlight is focused by a lens into a small area. If this focal point coincides with the bottom surface of the pool, the caustic band will be sharp, whereas if it doesn’t, the caustic band will be diffuse. On the other hand, the areas between the top of the waves have a concave shape and they act to disperse the light. This is why caustics are separated by areas that seem to be darker. In the video below, I have slowed down the network of caustics in a pool down to 240 frames per second. You can follow the caustic bands and see how they appear, disappear, merge, and separate continuously as a result of the pattern of waves on the surface of the water in the pool. I have previously posted about tensegrity structures. These are structures where the integrity of the whole is maintained by tension among its components. In the video below I show you how to build a simple but amazing tensegrity structure. The video includes an appearance by Science Cat! We tend to associate tail wagging with dogs. Almost everyone has seen happy dogs shaking their tails, and we have jokes and cartoons about it. We even have the phase “wag the dog” to describe when a small or less powerful entity takes control of a bigger or more powerful one. Apart from signaling that they are happy, dogs use their tails to communicate various messages about themselves, but, as it turns out, there are other species of animals besides dogs that use their tails to communicate things, and one of them is cats. Dogs evolved from wolves (Canis Lupus), which live in packs, so they tend to be social and expressive animals. However, domestic cats are evolved from the African Wildcat (Felix sylvestris lybica), which are solitary nocturnal animals, so the tail signals of cats are different from those of dogs. When cats curve and swish their whole tail from side to side it may indicate excitement or deep focus as when stalking a prey. This is a common predatory behavior especially if the ears are standing upright. However, a tail moving back and forth can also signal irritation or pain especially when associated with arched backs and lowered heads. When the cat only swishes the tip of its tail, it indicates that they are about to pounce or they are playing, but it can also signal that they are annoyed. If a cat wants to signal it is happy, it will stick its tail straight up, which in dogs is a sign of alertness, not happiness. In the video below Science Cat demonstrates how cats wag their tails. She is intensely looking at some birds in the bush outside while swishing her tail with her ears upright. One very common illusion employed in theaters, museums, shows and other venues is Pepper’s Ghost. The illusion is named after English scientist John H. Pepper who improved upon a previous ingenious but cumbersome illusion developed by inventor Henry Dircks in 1860. Pepper made the first demonstration of this illusion in 1862. The illusion relies on the fact that whereas light goes through most transparent glasses, a certain percentage of it is reflected by the surface of the glass. In the classical Peppers Ghost illusion, a glass is installed at an angle facing an audience. The audience can see with no problem the action taking place in the stage behind the glass. At some point an actor or an object is illuminated in a compartment that is located to the side of the glass in such a way that the light coming from the actor or object will bounce off the glass and appear to the audience to be coming from the stage as a ghostly apparition. In the photo below, I use a window to generate a version of the Pepper’s Ghost illusion, where I seem to be within the tree outside as a ghostly apparition.  In the video I used an exhibit at the 2019 Prague Quadrennial. I manipulated the see-through and reflection qualities of the glass window of the exhibit as well as the proximity of my phone to the glass, to create a Peper’s Ghost illusion. Note: the photo belongs to the author and can only be used with permission. |
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