Monday, December 31, 2007

Silver Fir Diffraction

The photo here was taken by Mónika Landy-Gyebnár. It shows light through the branches of a silver fir with thick, short grown needles. The camera was looking towards the sun and out of focus - just like in the spider web post of September. The curved structure is caused by diffraction. The image shows well-visible colours, and what makes the photo even more interesting is the horizontal lines across these coloured bands. Could it be some interference pattern created by the less spectacular slanting stripes on the side of the image? Or something else? More pictures

Saturday, December 29, 2007

Shadow Rays above Pithead Rig

In the morning of December 21, 2007, a beam of shadow rays appeared above the pithead rig of the German Minery Museum in Bochum, Germany.

The picture was taken at about 10 a.m., one hour after sunrise. As the sun elevation was still very low, the shadow of the pithead rig was projected upwards and became visible as a beam of shadow rays in a thin layer of mist near the ground. A similar phenomenon can sometimes be seen above a pylon or tower, but there only one single dark ray appears. The shape of the pithead rig, however, made a beam of four shadow rays appear.

Author: Peter Krämer, Bochum, Germany

Colours on fissures in ice

In the late afternoon of December 15, 2007, temperatures began to stay below freezing 24 hours a day for the first time (!) in this year. Already the next morning, many of the small puddles on a lane near our town Barsinghausen were covered with ice. Children enjoyed breaking these crusts of ice with their feet. But at some of the puddles which had frozen down to the ground, they had no success and just caused some fissures in the ice. These fissures showed extremely intense colours.

The colours are probably caused by interference. Light enters the ice and is reflected to and fro between the edges of the fissures. So there are differences in the time the light needs to cover the distance between the ice and the eye of the observer. This causes light waves to amplify or extinguish each other. This is what we perceive as colours.

There is no direct sunlight necessary for this effect (1 2), but it can increase it enormeously (3 4).

Author: Reinhard Nitze, Barsinghausen, Germany