Worlds in the Sky

The history of observational planetary astronomy (a rubric under which Sheehan also includes the study of the moon, other planetary satellites, and, very sketchily, comets and meteors) can be divided into three epochs: naked-eye observations, from the dawn of human history through 1609, although Sheehan does not pick up the story until the Greeks of the fourth century B.C.; telescopic observations, starting with Galileo in 1609 and continuing into the mid-twentieth century; and the epoch of observations from spacecraft, which dates from the Russian Lunik 1 in 1959. Sheehan’s summary of the first epoch, in which he touches on the seventeenth century theoretical work of Johannes Kepler and Isaac Newton, is extremely cursory. His discussion of the second epoch, although also relatively short, is more interesting, because it is informed by Sheehan’s experiences as a psychiatrist interested inperception and as an amateur astronomer. He understands how difficult and unreliable telescopic observations of planets can be. Much superior to the earlier discussions is his evaluation of what has been learned from spacecraft during the past generation or so. Almost everything that astronomers thought they knew about the planets in 1959 has been proven wrong. Supplementing the text area number of illustrations, two appendices of statistical information, and an excellent bibliography of historical monographs and nontechnical scientific accounts.

This is an accurate and interesting introduction to the current state of knowledge of the planets, and how astronomers have reached that state.