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uni'wissen 01-2014_ENG

Polarization describes the direction in which light waves strike out. The corresponding signatures of photosynthetic molecules, such as those of green and reddish leaves (above), are unmistakable. Moreover, the signatures of the leaves are clearly different from those of green and red sand (below). Photos: Svetlana Berdyugina ray of a light source – a sun or a light bulb – all directions are represented equally. Since no direction is predominant, such light is referred to as unpolarized. However, as soon as these waves shine through an obstacle or are reflected from a surface, they are polarized, meaning that they oscillate more strongly in a certain direction. This principle is also useful in everyday contexts, such as for anti-glare sunglasses, whose lenses do not allow light with a particular polarization through. In this way, car drivers can protect themselves from being distracted by reflections from puddles on the street. This is also why pho- tographers attach polarization filters to their lenses, and polarization filters are also used in 3D glasses for movie theaters: The image for the left eye is projected onto the screen with light whose polarization is different from the light with which the image for the right eye is projected. The filters in these special glasses only allow one kind of light through. The polarimeters Svetlana Berdyugina and her team are developing basically follow the same principle as these polarization filters. The main difference is that the scientists do not hold them in front of their eyes but build them into powerful telescopes. These instruments have become so sensitive that they can detect a po- larization of only 0.001 percent in the light they are measuring. In 2008 Berdyugina and her colleagues became the first scientists ever to detect light reflected by the planet HD 189733 b, which is located 63 light years away from Earth; a light year is roughly equal to 9.5 trillion kilometers. “Experts were naturally skeptical of our interpre- tation of the data initially,” says Berdyugina, “but that is healthy scientific skepticism. When the prediction we made in 2011 about the color of the planet was confirmed by an independent source, it of course still gave us great satisfaction.” Berdyugina had deduced with the help of more precise polarimetric data that HD 189733 b would appear bright blue to the naked eye. In 2013 Prof. Frédéric Pont and Dr. Tom Evans succeeded in 6