Asimov gives so patient and detailed a survey of the mapping of the heavens, the naming of stars, and (especially) the different ways of measuring their distance, size, and luminosity that Alpha Centauri becomes less the subject than a focusing point for a general astronomy lesson on the order of his younger "How Did We Find Out. . ." series. (Contributions of Ptolemy, Newton, and Doppler are only a few of those surveyed in passing, and there are numerous tables, including "Eccentricities of Binary Systems" and "Transverse Velocity of Some Stars.") We do learn though that Alpha Centauri, an "unremarkable star" like our sun, is actually two individual stars--or three, with the dim (eleventh magnitude) third component that qualifies it as a "ternary" star. Speculating on "life among the stars," Asimov concludes that among the possibly habitable ones the Alpha Centauri system is not only by far the closest but also the most probable--but getting there "won't be easy." As the one-way trip would take more than 4.4 years at the speed of light and 7,400 years at ten times the speed of our current, fastest rockets, it will be a while before even Asimov can come up with a Land and Peoples of Alpha Centauri.