The systematic search for stellar multiplicity by observations of lunar occultations began in 1969. David Evans will review a large portion of the data collected since then in the second paper of this session. Here we will outline the historical development of the technique and comment on its limitations, contributions to double star research, and future improvements.
Sir John Herschel (1865) may have been the first to suggest that “a double star, too close to be seen divided with any telescope, may yet be detected to be double by the mode of its disappearance.” However, the visual discovery of duplicity by occultation is not sufficient, for the observations are not subject to analysis after the fact. The power of the occultation technique was realized more than 100 years after the suggestion, with the application of photomultipliers and electronic digital data handling. Whitford (1939) took the first step in using a cesium photo tube, oscilloscope, and moving film to record the occultations of Beta Capricorni and Upsilon Aquarii. The resolution of the spectroscopic binary Beta Capricorni was discussed, but he concluded his data were not able to resolve it, an observation which was later accomplished at several observatories and summarized by Evans and Fekel (1979).