Abstract
Making Stars Physical is a welcome addition to the growing body of work on the lives and scientific contributions of the prolific Herschel family. Its focus is the icon of nineteenth-century science, polymath John Frederick William Herschel (1792–1871), but it is not a biography in the strictest sense. As author Stephen Case explains, his goal in this work is “to establish the pivotal role that John Herschel’s career played in the prehistory of astrophysics, transforming the stars from the celestial placeholders of positional astronomy to the physical objects that we conceive them to be today” (p. 231).
Using correspondence, diaries, and other contemporary resources, Case documents Herschel’s efforts to revisit his father’s sweeps of the northern heavens and extend them to the southern sky in search of double stars, variable stars, and nebulae. It was a lifework for which he was uniquely suited, but it was not a vocation to which he aspired.
Born when his renowned father, William, was 53 years old, John spent his early years surrounded by adults, including his doting Aunt Caroline. A patchwork of private schools and tutors prepared him for Cambridge where he excelled in mathematics and developed a lifelong love of chemistry. After graduation, John announced his intention to pursue a career in law. Indeed, he showed little interest in astronomical work until his aging father prevailed upon him to return home as an apprentice and master the skills necessary to complete the elder Herschel’s celestial surveys. The dutiful son complied and set to work.
Even the most extensive catalogue is little more than a cluttered cabinet of curiosities unless its contents can be examined, verified, and analysed by others. Case details how John, encouraged and guided by his aunt’s example, painstakingly recorded the positions and salient physical characteristics of the celestial bodies he observed so that others – professionals and amateurs alike – could independently locate, assess, and describe each one. Like his father, he considered stars less as points on a map and more as individuals with characteristics that could be categorized and watched over time for signs of change. He encouraged broad participation in what he envisioned as a global collaborative effort to collect observations that were not merely anecdotal but scientifically useful. To that end, he designed, printed, and distributed standardized forms on which anyone, anywhere could record their findings.
In his final chapter, Case nicely fits the details of Herschel’s long, productive, and influential career into the wider context of nineteenth-century astronomy and the rise of astrophysics. A decade before John was born, his father’s discovery of a new planet breached the physical borders of the known solar system. By the turn of the century, William’s monumental census of celestial species was quietly eating away at the walls surrounding astronomy’s garden, admitting new field workers to tend it, and stimulating the development of new tools and methods. When John assumed his father’s mantle in 1816, the science of astronomy was still largely wedded to tracking the movement of Earth’s solar system companions against the array of carefully plotted background stars, but its blurring boundaries signalled the emergence of something new.
By mid-century, Herschel’s views reflected the complexity, strengths, and limitations of the state of contemporary astronomical knowledge. He considered his father’s discovery of Uranus a “trifle” compared to the far-reaching theoretical and methodological implications of his canny recognition that some of the hundreds of double stars he had catalogued were likely pairs bound by mutual gravitation. Providing convincing evidence that a fundamental law of terrestrial physics is truly universal was, in John’s opinion, William’s most significant scientific contribution.
Despite advances in spectroscopy over the first half of the nineteenth century, Herschel doubted that astronomers would find it to be as useful an analytical tool as had chemists and physicists. Spectroscopic investigations conducted in terrestrial laboratories used bright light sources. Results could be subjected to controlled testing by other means. By contrast, celestial light sources were faint, their spectra so feeble they often tested the limits of human vision. Even more problematic in Herschel’s view was the lack of an undergirding explanatory theory of spectra to aid in their interpretation.
As Case shows, John Herschel successfully leveraged his notoriety and the fruits of his labours to harness the fertile flux that lay hidden beneath nineteenth-century astronomy’s public façade of stability and uniformity of purpose. He expressed his views with authority in both popular and professional print, creating a canon that was repeated and widely circulated by others throughout the nineteenth century. His influence encouraged amateurs and professionals to study the diverse physical characteristics of the stars themselves, to embrace such work as a legitimate means of extending known terrestrial laws of nature to the celestial realm, and ultimately to resolve the intractable mystery of the true nature of the bodies that populate it.