Friday, January 30, 2009

Kitchen optics

An everyday kitchen can provide ample opportunities for observing optical phenomena, and as Mónika Landy-Gyebnár and Ágnes Kiricsi are not only good housewives but keen observers of such beauties, they always keep their eyes open for a chance of photographing something interesting while doing their household duties.

When you decide to drink your coffee in the early morning sunlight that just reaches your kitchen window, you might be lucky to get its steam of equal droplet size, and opening your eyes with the first sip of coffee you notice the colours of the drifting steam. You must have another sip to be sure that you really see the scattered sunlight and the display of iridescent colours.

If you use a spoon to stir your coffee with, don't run to the dishwasher immediately, but be a bit negligent, and wait till the coffee dries on it.

You may discover spectral colours again: patterns of thin film interference. Could it be the coffee's volatile oils or bacteria signalling problems of mouth hygiene?

Bisquits are always good to crunch with the morning coffee. Most of them are packed in a small cellophane bag that we can easily drop aside at the table by the window. And here comes the sun again - as its rays fall on the empty sachet, birefringence produces the well-known spectral colours again.

Not only human beings need a refreshment in the morning - our plants are also thirsty. And not only cellophane sachets are prone to showing birefringence, but transparent plastic flowerpots, too.

We have to pack a sandwich for the workday, maybe a good slice of ham - oops, the ham is also showing the spectral colours! The tiny (a muscle cell is about 10-80 microns in diameter), regularly arranged cells of the meat behave like the water droplets of clouds.

When the office hours are over, we still have some activities at home: for example making dinner for the family. Let's treat them with some meat balls, fried delicious in hot rainbow-coloured oil. Yes, rainbow coloured, as the afternoon sun still shines in, and the transparent oil bottle is placed in front of the window. You don't necessarily need a usm filter (or a usm sieve :)) to see the caustic patterns.

But be careful! Never cover hot food with a foil, otherwise they might produce colours again. First spectral ones on the foil, which we are happy about, but later a sickly shade of green on the meat itself. In this second stage, don't hesitate to throw the food into the dustbin.

Towards the end of the day, the work of the housewife has not ended yet. She's still on duty in the kitchen, looking at the pile of dirty dishes that has been produced.While the hot water gathers in the sink, it also steams a bit. There's no evening without a good streetlamp corona - you only have to look outside for a moment! The hot vapour has precipitated on the cold glass of your kitchen window, so the long day's last phenomenon wishes you good night with a colourful display.

Let's hope that reading so much about these household duties won't cause you nightmares of mugs carelessly washed up, and that one evening a brave man sits in front of the computer, and writes an article about the optical phenomena observed during his weekend-long tinkering in the workshop.

Sunday, January 25, 2009

Shadows on ice crystals

During the cold spell in the middle of January, some of us in Hungary started "experimenting" with snow crystals. As surface halos had been observed for several consecutive days (see the images of the odd radius surface halos by Ákos Ujj: 1 - 2 ), our basic idea was to find out whether we would see the trace of the 22 degree halo if we simply threw up the snow crystals covering the ground. Interestingly, the answer was yes. It was really exciting to observe that 22° from the sun, the crystals were glittering in spectral colours, and they faintly drew the form of the halo. Unfortunately, I was not so lucky with photographing the effect. All I could capture was the streetlamp casting its shadow on the crystals thrown and kicked in the air by Alexandra Farkas.

In the evening, however, Károly Vicián was much more successful. He had similar methods, but with longer exposure time, he did not only manage to photograph the shadow of the broom that was used to cover the spotlight, but the halo thus forming, too.

Saturday, January 17, 2009

Perigee Moon

This photo was taken by Claudia Hinz at the evening of Jan. 11th, 19.35 CET from Mt. Wendelstein (1838m), Southern Germany. The full Moon in this night was extra bright. Dr. Elmar Schmidt of the SRH University of Applied Sciences in Heidelberg, Germany, used an absolutely-calibrated photometer to precisely measure the moonlight and found it more than 50% brighter than that of a typical full Moon.

1. The Moon was at perigee, the side of the Moon's elliptical orbit closest to Earth.

2. The Earth-Moon system was near perihelion, the side of Earth's elliptical orbit closest to the sun. Extra sunlight increased the reflected luminosity of the Moon.

3. The Sun-Earth-Moon trio were almost perfectly aligned. This triggered a strong opposition effect an intense brightening of the lunar surface caused by the temporary elimination of normal shadows.

4. The weather conditions were optimal for photometry due to the clean and dry arctic air (its relative humidity being less than 10% at the moment of the photo). This resulted in only clear air scattering of moonlight with no extraneous glare as evident in the completely blue night sky. The brightness of the mountain landscape was additionally increased because of the reflection from the snow.

Elmar Schmidt details the relative contributions of each factor in his full report.

Text: Elmar Schmidt & Claudia Hinz

Effects in cloud bows caused by perspective

In the morning of December 12, 2008, I coud observe a cloud bow on a stratocumulus layer, which was kind of perspectively cracked. Due to the ruggedness of the cloud surface it seemed as if there was a deep horizontal notch on the left side of the cloud bow.

But also this moonlight cloud bow, taken on September 9, 2008, seems to have vertical indentations and also an elliptical shape caused by the horizontal projection upon an uneven surface.