Shadows and Light

Ordinarily, an object's image can be formed by bringing light rays to a focus, either by refraction (using a lens) or reflection (using a mirror). But what can you do if the type of light you're interested in won't reflect or refract? This is the problem facing astronomers who study high energy X-ray and Gamma Ray radiation. One solution is to use a technique called "coded aperture imaging"; in coded aperture imaging, a "mask" is placed in front of the detector (usually a CCD is used as the detector), and an image is reconstructed by studying the variations in the patterns of shadow and light produced on the detector by the mask. The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) will conduct high resolution spectroscopy and wide-field imaging of X-ray and Gamma Ray sources. To image these sources, INTEGRAL will use a coded mask instrument called IBIS (Imager on Board INTEGRAL Satellite). The upper image of the champagne bottle and the glass in the figure above was produced by one of the IBIS detectors called the ISGRI; the lower image shows how these objects would look using an ordinary refracting imaging system (your eye). INTEGRAL is the second Medium Sized Mission of the European Space Agency's Horizon 2000 scientific program.

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Each week the HEASARC brings you new, exciting and beautiful images from X-ray and Gamma ray astronomy. Check back each week and be sure to check out the HEAPOW archive!

Page Author: Dr. Michael F. Corcoran
Last modified April 12, 2000