Information-Processing Systems in Radio Astronomy and Astronomy

Until a few years ago, the application of information theory to the process of gathering astronomical data proceeded in an ad hoc fashion, if at all. Each experiment was designed to display the quantity with which it was concerned in the simplest, most direct fashion. More recently, the great complexity and cost of large optical and radio telescopes has made it manda­ tory that they be so designed to serve as many purposes as possible with high efficiency. This is facilitated if the maximum amount of information coming from the sky is preserved to a rather late point in the chain of processing the information. Some sophistication must now be used to efficiently extract the wanted data from a general format. The earliest astronomical observations were made visually, where one can measure only the positions and brightnesses of the stars (and the colors of the brightest) and the brightness distributions of the extended objects. Of the extended objects, only the Sun, Moon, and planets are of much inter­ est visually in a small telescope, and these were adequately represented by sketched maps from the time of the earliest telescopic observations. Perhaps the most successful quantitative adjunct of measurements of this type was the introduction, by Wolf, of the relative sunspot number in 1848. The most comprehensive and useful series of visual measurements of stars is the remarkable effort of Argelander (1859) and his assistants, who, in the space of 11 years beginning in 1852, made, reduced, and published approximately 700,000 observations of 324,198 stars, which comprise the BD Catalogue. Visual observations are now primarily used only in the measurement of close double stars (see the review by Van den Bos 1956). The rate of accumu­ lation of data by visual observers is sufficiently slow that it may easily be analyzed by the traditional graphical and arithmetic methods, although in practice it is desirable even here to program the reductions to lessen the labor required to achieve an impartial solution.