Electron Astronomy

The huge, complex telescopes of modern astronomy have a simple purpose: to concentrate light. Their mirrors (up to 200 inches in diameter) and lenses catch a wide bundle of light rays from faint stars or nebulae and cram them together at a small focus on a sensitized plate. Last week two French astronomers, Andre Lallemand and Maurice Duchesnes, were showing off a new wrinkle in astrophotography. Instead of depending on the original starlight to make the photographic impression, they plan to amplify the light's energy before it reaches the plate.

The image of the object to be photographed is first focused on a glass plate covered with an antimony and cesium compound, which gives off electrons when struck by light. At every point in the image electrons are knocked loose. Off to a slow start, they are whisked away at tremendous speeds by a powerful electric field. Then they are focused by a magnetic lens (as in an electron microscope) to form a new image on a photographic plate. The speeded-up electrons have taken energy from the electric field and form an image about 100 times stronger than the original light-image.

So far, the new method has been tried only in the laboratory. Among their test shots, the inventors have two pictures of a glowing filament covered by a dense filter that made it invisible to the naked eye. One picture, taken directly on a photographic plate, showed only a dim trace of the filament after a six-hour exposure. The other, taken with speeded-up electrons, showed the whole filament clearly after only four minutes.

Next month the new method will be tried astronomically; its inventors hope that it will transform the biggest telescope of the Paris Observatory (24 inches) into the equivalent of a 240-incher, and make it possible to photograph billions of faint stars never detected before.

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