Twilight - the space between day and night (without vampires)

How many painters have attempted to capture the gradiated hues of a sunset in pigments? It takes true mastery to get translucent fleeting colours from flat pigments; some artists do it exceptionally well, but most don't. Detailed observations of actual sunsets is the key: what colours go where? How do a few clouds change things? Cameras can capture some aspects of a sunset, but often miss the nuances. With my digital camera, I took this picture near the end of my drive to Winnipeg last summer – the sunset was much more stunning in person. However, nothing beats sitting on a patio somewhere with a view (perhaps with an accompanying beverage) and watching day turn to night.

Sunsets are a spectacular end to the day – however the entire process of shifting from day to night is called twilight. According to a book published in 1966 by Georgii Rozenberg (called 'Twilight' without a single mention of vampires – I like to read old science books): The term twilight refers to the entire complex of optical phenomenon that take place in the atmosphere when the sun is near the horizon. It occupies the interval separating daytime conditions of illumination from night.

I live far enough north to get reasonably extended twilights. The downside is that I live far enough north that twilight can start in the late afternoon on the shorter days of the year. Every twilight is unique and the shift from day time brilliance to more subdued hues feels almost magical. During twilight, the illumination at the ground decreases by a factor of a billion. If seen from space, twilight covers a global swath separating day from night. Twilight happens because the earth is rotating – so it will occur on every rotating planet with an atmosphere.

Looking up at the sky has been a pass-time for eons. However, early in the 21st century, before spaceflight was common, a keen interest in studying twilight emerged to provide details about the composition of the atmosphere – useful to know if you are trying to communicate by radio.

Many interesting phenomenon occur each twilight (I'll write more in other posts), however sunsets are the most obvious. Atmospheric optical properties are responsible for the vivid colours of sunset. Specifically, the amount of water vapour and dust play a huge role. In 1863, atmospheric scattering and attenuation of light were shown to produce the sunset colours. Since entire books have been written on sunsets, so my description will be brief.

When the sun drops towards the horizon, the sunlight must pass through more atmosphere. Since shorter wavelengths of light are scattered preferentially (see Rayleigh scattering post), the sun appears in redder tones (red is at the long end of the colour spectrum) and the near-by sky takes on yellow and orange hues. When the sun is about 5 degrees below the horizon (like in my picture above), it is out of sight to an observer on the ground. The sky above the horizon remains brightly coloured in deep reds while mountain tops and clouds are bathed with crimson and purple light.

A cool home experiment for generating a sunset in a glass can be found here.

Bloody colours

To a bloody war and sickly season - the traditional Thursday toast of the British Navy.

Since I've already written about blue (here and here), a friend suggested I write a post on redder colours, specifically ones named after bloody battles. I only found two: magenta and solferino – both are purplish red colours, perhaps even the same colour. Magenta and Solferino are both towns in Northern Italy that were caught up in the second Italian war of Independence at the same time synthetic dyes were being made from coal tar for the first time. Magenta as a colour name is still in common use, while Solferino was the more important battle. A witness to the battle of Solferino, Henry Dunant, found it so horrible he began a campaign that ultimately resulted in the founding of the Red Cross.

In 1859, Emmanuel Verguin's experiments with aniline dyes (ie the ones from coal tar) resulted in a rich crimson red. He called the colour fuchsine after the fuchsia flower and it was an instant hit. This was a prominent colour of the uniforms at both the battle of Magenta and Solferino, both in June 1859, so I don't know if the colour took these names because of the uniforms or the bloodiness of the battlefields (I've found references both ways). A few years later, the colour's name was once more changed, this time to rosaniline, but magenta is the name that stuck. A arsenic acid oxidation process was required to make this dye causing some of its wearers to be poisoned – leaving magenta even more bloody. (For more details of synthetic dyes 'Mauve' by Simon Garfield is a good read)

If you took a good look at the colour spectrum of light, magenta wouldn't be found. Magenta is considered an extra-spectral colour because it cannot be generated by a single wavelength of light. It is formed in our minds when there are equal parts of blue and red light (in truth colours only exist because our brains perceive them).

A beach

My favorite beach is one I used to go to when I was a kid. Not a traditional sandy expanse, this beach was far enough off the beaten path that it was generally deserted – an ideal location for my imaginary world to thrive.

To get to the beach I would walk down a blackberry lined sandy road where the lapping of waves and calling of seabirds would reach my ears long before they came into view. Once I reached the end of the road a small path was cut into the broom and blackberries. I would navigate this steep path down a short cliff. From there, I could see the undulating surface of the sea extending in all directions until it was broken by a blue-toned landscape a long distance off. Huge driftwood pieces, tossed ashore by winter storms, now blocked the path. I remember balancing along these logs until I reached a field of tiny stones. Beyond the stones was my favorite part: a wide band of sandstone formations. Unless it was the lowest of low tides, beyond the sandstone lapped the waves. When there was an extreme low tide, a new landscape of seaweed covered rocks and tide pools was exposed.

The sea-worn sandstone captured my imagination the most. Each shape could be an fantastical dimpled animal large enough to sit on and I could ride the dusty yellow beast with sandpaper textured skin anywhere my imagination could devise. Or the shapes could be mushroom formations rising up from a pool of lava, forcing me to leap between each one to get to the other side. Or the shapes could be worn down fortifications of an ancient castle, giving me a place to hide from my enemies. Some shapes had dimpled pickets that held treasures like tiny shells and stones. In some places shallow pools that were warm enough to wade in separated the shapes. These pools would be home to seaweeds, bullheads (sculpins), crabs and snails; the pools that only existed at low tide housed anemones and starfish.

The maze of rough sandstone shapes could entertain me for hours – and held different objects to discover every time I was there. Some days abandoned fishing floats would wash up, other days there would be uniquely shaped driftwood that could be imagined as tridents, swords or crutches. Always there would be seabirds watching from a safe distance and cackling amongst themselves.

I've never seen another beach with the same type of sandstone formations as the one from my childhood. That childhood beach actually exists, but I haven't been there for years. I've gone back to other places that held magic for me as a child, but now they are just places, no longer manifestations of my imagination. So I won't physically visit that beach of my childhood, instead I'll just visit the memories.

Ships of the desert

Years ago I wrote a story about a woman crossing the Sahara Desert. Part of the reason I put her there was my discovery that native desert folk could look at a camel's footprint and tell its gender. I have no idea if this is true because I've never been to the Sahara, or anywhere where there were people identifying a camel's gender from footprints. To be honest, the closest I've been to a camel is a zoo (the warning about spitting sign ensured I didn't even get close to the fence). According to the reference I found years ago (and can't find now), camels of different genders were used for different purposes, so the pads of their feet would wear differently.

The idea of camels as 'ships of the desert' brings to my mind lines of camels carrying exotic goods (in my mind each camel is swarming with their 'horse fly' equivalent). Like every school kid knows, a one humped camel is a dromedary and a two humped camel is a bactrian; I'm thinking about the dromedary camel. These camels originated in Arabia where they were domesticated over 4000 years ago. From there people took them to North Africa, India, Pakistan and Australia – then even further afield as I've seen them in North American zoos.

A camel can carry up to 600 lbs of freight up to a distance of 160km a day (a fact I found in a children's book), making them outstanding pack animals already evolved for a desert environment. They can be speedy; racing camels can get up to 33 km/hr for a 10 km race. Back to their footprints: they have broad feet that are heavily padded to allow them to walk stably over hot sand. I guess if there is some humidity, they could make a pretty distinctive footprint. But, if someone told me they could tell the gender of the camel from that footprint, I would assume they were pulling my leg.

Black jackets and being seen – or "How Not To Be Seen" for Monty Python fans

I recently bought a new jacket because my old one fell apart. I wanted a bright colour, easily seen by traffic when I walk to work on rainy, gray days (for obvious reasons). I also wanted my new jacket to be waterproof, again for those rainy days. I'm not much of a shopper, but I did shop around and the only jacket that I could find that met my criteria was black. So now I have a black jacket – the exact wrong colour for high visibility. As a teenager, I had a khaki jacket (army surplus) – a colour designed to blend into wilderness surroundings. I'd often wear this jacket camping. To be seen, I wore nuclear orange gloves that my grandmother had given me. From a distance often all that could be seen of me were the gloves. I actually loved the juxtaposition of my khaki jacket and nuclear gloves. Which brings me to how things appear to "stand out", using sharp contrasts like my gloves.

Distinctive shapes also stand out. For example, our brains are hard-wired to see faces, even in bizarre places like stucco walls and clouds. For this reason, soldiers often paint disruptive green patterns across their faces when they want to vanish in the woods. Straight lines where they shouldn't be also stick out as nature generally doesn't have straight edges. Ever looked at a satellite photo of a wilderness area and had the square shape of a cabin pop out? Movement sticks out. I can find escaped crickets (we keep critters that eat crickets) on out cricket coloured carpets because they move. So, if you are hiding from bad guys: stay still.

On my walk to work I want to be seen. My nuclear orange gloves vanished years ago so I can't rely on them. A retroreflector is an option which is just a good reflector set up to bounce the light right back where it came from irregardless of orientation. The shine from a cat's eye when light hits it is an example. One type of retroreflector is a corner reflector, which is three mirrors put together like the inside corner of a cube. Since many small versions of retroreflectors can be put together as a thin sheet and attached to a fabric, clothing can be made from them. On a dark, rainy day I could wear a retroreflector band around my wrist which would bounce the light of car headlights back towards the driver, warning the driver of my presence. So my problem is solved, I need to find retroreflector wrist bands: but where else are retroreflectors used?

Retroreflectors have made their way to the moon both on American (Apollo 11, 14 and 15) and Russian (Lunakhod 1 and 2) spacecraft as a way to determine the distance between the earth and moon. This is done by aiming a laser on earth at the retroreflector and measuring how long the light takes to return back. This method has found the average distance from the earth to the moon is about 385,000 km. All the retroreflectors on the moon are still in use. They are the only Apollo experiment still returning data from the moon (I don't know if there is Russian gear other than the retroreflectors still transmitting, but I doubt it) and has resulted in and improved knowledge of the moon's orbit.

On a tangent... somehow the Russian Lunokhod 1 rover got lost. On November 17, 1970, Luna 17 arrived at the moon and released the Lunokhod 1 rover to explore. This rover trundled over 10 km, taking samples of the lunar surface and transmitting pictures, until its power ran out at year later. Since a retroreflector was mounted on the rover, scientists were able to keep track of it with lasers from earth until 1974. Then they lost track of it (not sure why because it was no longer moving). Recently, NASA's Lunar Reconnaissance Orbiter spotted the rover's tracks (remember, the only movement on the moon has been us and there is no wind to cover tracks) and was able to pinpoint the rover's location. On 22 April 2010, a laser was bounced of its retroreflector once again.

So a retroreflector turns out to be an excellent way to be seen even from really far away. However, if you are really good with your optics, a retroreflector can be set up that will render one almost invisible.

Sea foam – and why it can be bad for birds

The word “sea-foam” has a feminine mystique to it. I picture it used for frilly prom dresses and girly princess rooms. In the real world, sea foam is never the pretty light aqua colour of paint chips, instead it looks like dirty cappuccino foam – a yellowed off-white often with chunks of stuff in it. As the sea sloshes, salts, chemicals, dead plants, decomposing fish and sea weeds are churned into sea foam. Individual bubbles link together, and when a surface wave passes these bubbles they mass together as they swirl upwards to make foam on the sea surface.

Sea foam on the water's surface changes how wind energy is transferred into the water. This transfer of energy is a type of friction, called the wind stress, and it can play a part in important oceanographic processes such as currents and upwelling. What sea foam does is add another layer between the wind and ocean, so instead of the wind pushing the water, the wind has to push the foam and then the foam pushes the water, which is a much less efficient process. Sea foam can do much worse things.

In the coastal ocean red tides occur, which is a dangerous form of algal bloom. A red tide is better described as a Harmful Algal Bloom or HABs, because HABs aren't all red and not all red tides are HABs. Specific phytoplankton (little water plants) full of toxins are the culprit and are bad news for shell fish and anything that eats them, like us. Recently, migrating birds along the Washington State coast were found dead in large numbers at the same time as an HAB occurred. The birds weren't poisoned; instead they were freezing to death. Why? One or more of the HABs causing phytoplankton were getting churned up into the sea foam. Birds would rummage around in this foam getting themselves covered in it, because normally sea foam isn't a danger to them. But in this case, the phytoplankton-laced foam coated the bird's feathers is such a way that they lost waterproofing and insulation, so that the poor birds froze.

Foamy frothy fun

Most of my days end with a long soak in a deliciously hot bubble bath. I don't need fancy scents, instead I enjoy the heat of the water and playful texture of the bubbles. Bubbles rise up as a mound ringing the stream of water from the faucet. Further away, bubbles slide into irregular shapes reminiscent of fictitious moon bases and futuristic homes. If it's really quiet, the muffled pops as multiple bubbles end their existence is audible. In addition to a relaxing end to a day, my bubble bath is an example of a foam.

Foams form when billions of tiny bubbles are packed together within a solid or a liquid. Irregular sized bubbles are common in all foams except the most idealized ones. Like what happens for individual bubbles (check out my bubble post), it's surface tension that helps keep a foam stable. Liquid foams break down eventually – there are even chemicals on the market to make this process go faster. Gas can diffuse from small bubbles into large ones and eventually out of the foam, or gravity can drain liquid out the bottom making bubbles so weak they pop on top.

A Belgian physicist, Joseph Plateau (1801-1883), figured out the basis of what we know about soap films and foams. His diverse interests also included spending time with moving image illusions like the action one sees when using a "flip-book". Back to soap film, Plateau came up with a series of laws to describe stable foam structures (foams that don't follow these laws tend to rearrange themselves until they do). They are:
1.Soap film surfaces are smooth.
2.The soap film curvature is continuous and constant along the entire a surface.
3.When three or more bubbles connect together, they will shift around until each line only contains three bubble-wall intersections – called a Plateau Border. With matching surface tensions all three angles are 120 degrees, the most efficient option.
4.Only four Plateau Borders can meet at a point.

Foams form in nature. Examples include: sea and river foams, and the foaming at the mouth of a rabid dog. There are fish, such as gourami and Siamese fighting fish, that blow a mass of bubbles coated in saliva to house their eggs. In the same spirit, some species of frogs make foam nests to lay their eggs in. These nests may be constructed in crevices, on the surface of water, or on forest floors.

Beyond bubble baths, soaps can be whipped to form a lather with bubbles so small they hardly can be seen. This idea was extended into modern shaving foams where a compressed gas is rapidly decompressed to expand a cream into a foam. Foams can also be hardened into permanent structures like insulation and flotation devices. Ceramic can be made into foams useful for acoustic insulation, absorption of environmental pollutants, and the filtration of molten metal alloys among other applications. Cement foams are used as a light-weight building material with good insulating capability. Even metals can be manipulated into becoming a foam. Metal foams are used in exhaust mufflers as they a great at dampening noise. They also make efficient materials for heaters and heat exchangers since they have so much surface area.

We eat a lot of foams: they can add a light texture to an angel food cake, or be tasty in the form of whipped cream and meringues. Breads are often a foam as the yeast produces tiny bubbles of gas which causes the dough to rise. One of the best foams is the head that forms when a beer is poured into a glass; this foam is made by which is made by carbon dioxide bubble rising to the surface. For the best head on your glass of beer, chose a wheat beer instead of a barley beer.

Note: there is an optimum foam combination of wheat beer consumed in a bubble bath – use with caution.

Tiny bubbles

Anyone remember the show “That's Incredible!”? It was on in the early 80's. I watched it as a kid (and yes I'm dating myself as the show went off the air in 1984). One episode I remember vividly: The hosts hyped how this man could make a square bubble, which I suppose what hosts are supposed to do. Since all the bubbles I had ever seen were round, I was really curious how a square bubble could be made (and I wasn't yet jaded about TV). I was expecting the square bubble to be free-floating by itself, so I was kinda disappointed in how it was done. The “performance artist” blew a bunch of connected bubbles (I forget how many). Next he took a long inhale from a cigarette, then stuck a straw between the connected bubbles and filled the space with the smoke. The filled space was in the form of a cube, and I felt tricked.

A short lived creation, soap bubbles hold a sphere of air with a thin film of soapy water which is formed by surface tension. Spherical shapes are preferred (really large bubbles can end up forming elongated shapes from air currents) because a sphere is the smallest surface area possible to contain a specific volume of air. The soap film surface tension is strong and flexible enough that waves can travel along the surface and is so thin the surface appears iridescent.

Surprisingly, soapy water has less surface tension that water alone and is needed to keep the bubble stable. As a bubble is formed, the soap film stretches decreasing the concentration of soap which increases the surface tension. This mechanism is called the 'Marangoni Effect' and occurs when a surface tension gradient (that is regions of greater and lesser surface tension) causes liquid to move away from areas of low surface tension. The soap acts as a stabilizer by letting the thinnest parts of the film to have the strongest surface tension thus keeping the bubble together.

What happens when two bubbles stick together? Well, they will arrange themselves in such a way that minimizes the surface area. Bubbles of different sizes will end up with a bulging internal wall into the larger on as smaller bubbles have higher internal pressure. If they are the same size, the internal wall will be flat - a phenomenon exploited by the cube-making bubble performer.

So sneaky internal bubble-wall cubes aren't so impressive. How about antibubbles ….