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Arrays have physical limitations that interfere with their inability to measure the largest scale structure of objects. There are two reasons for this. The first is that the field of view of an array is dependent upon the size of the dishes comprising that array. Therefore, when an object is larger than that field of view, astronomers have to make several observations in order to compile an image of the entire object.
The second reason is the simple fact that the dishes in an array cannot be placed closer together than their diameters, otherwise they would physically overlap. For this reason, important information may be lost between the gaps.
To obtain larger field-of-view images, astronomers combine data from several overlapping observations. For each observation the array is pointed in slightly different direction, thus imaging different areas of the object. Each "pointing" is set so that its field of view overlaps a bit with the preceding one. This enables astronomers to combine the data from consecutive pointings into a composite image spanning a much larger field of view.
While mosaicing will be used mainly to improve field-of-view, the novel technique will also enable astronomers to merge single-dish observations with those from the array, thus regaining information that otherwise would have been lost.
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