Nakaya was born in 1900 and died in 1962, a lifespan that bracketed nearly every upheaval of twentieth-century Japan. He trained as a physicist, and it was at Hokkaido Imperial University, in the heart of Japan’s heavy-snowfall region, that he began the work for which he is still best known. Snow crystals were an obvious local phenomenon but a difficult experimental subject: natural snowflakes fall from clouds whose temperature and humidity conditions can only be guessed at, so relating a crystal’s final form to the conditions that produced it seemed almost impossible. Nakaya’s insight was to bring the cloud into the laboratory.

In 1936, after years of painstaking trial and error, Nakaya produced the world’s first artificial snow crystal in a cloud chamber. The achievement was more than a stunt. By systematically varying temperature and the degree of supersaturation of water vapor, he could grow crystals on demand and observe how their morphology changed. Needle-like crystals appeared in one regime, plates in another, and the celebrated branched dendrites in a third. The result was a compact summary of the dependence of snow crystal shape on the conditions of formation, a chart that has become known to atmospheric scientists everywhere as the Nakaya diagram. It remains a foundational reference for anyone studying how ice grows in clouds, and it underpins modern understanding of the microphysical processes that govern precipitation.

The artificial snowflake also carried a philosophical message that Nakaya would repeat throughout his writing career. He famously described snow crystals as letters sent from the sky, messages written in a hierarchy of characters, words and sentences that a patient observer could learn to read. The phrase captured his conviction that the laboratory and the sky were not separate realms: controlled experiments could decode what nature wrote, and the decoded message belonged to everyone, not just to specialists. That conviction would drive a second career that made him, in the words of his biographers, something like Japan’s answer to Carl Sagan.

The new study pays particular attention to two of Nakaya’s most ambitious magazine essays, which give the paper its title: World of the Black Moon and World of the White Moon. These were vivid first-person accounts of mid-twentieth-century scientific field expeditions, and they show Nakaya doing something that science communicators still strive for today, placing the reader inside the daily experience of research. World of the Black Moon drew on his travels to Hawaii, while World of the White Moon recounted his fieldwork in Greenland. Together they form a literary diary of an era when international geophysical science was expanding rapidly and when a Japanese writer could carry readers to places almost none of them would ever see.

The Greenland essays had particular weight, because Nakaya’s Greenland work was serious science as well as journalism. In the 1950s he began collaborating with the US Army’s Snow, Ice and Permafrost Research Establishment, known as SIPRE, investigating the physical properties of glacial ice. He took part in fieldwork in Greenland during the pioneering years of the deep ice coring project there, one of the earliest systematic attempts to read climate history out of layered polar ice. The cores recovered from the ice sheet in those years opened a new window on past climates, and Nakaya’s studies of ice deformation and crystal structure contributed to the young science of glaciology at a moment when its methods were still being invented.

Remarkably, World of the White Moon also contains a very early description, written for the general public, of the problem of anthropogenic climate change. At a time when the greenhouse effect was discussed almost exclusively in technical literature, Nakaya explained to magazine readers how human activity could alter the global climate, connecting his own observations of ice and snow to a planetary question. The biographers argue that this makes the essay a landmark in Japanese popular science writing, and it gives the piece an urgency that reads strikingly today, decades before climate communication became a global industry.

Nakaya’s literary range extended well beyond his own expeditions. He was a prolific essayist whose articles appeared regularly in Japanese magazines and were repeatedly collected into books, many of which remain in print more than sixty years after his death. His subjects ranged across science, culture and everyday life, and his tone was conversational rather than didactic. He treated his readers as intelligent companions rather than students, an approach that earned him a broad and loyal audience. The new study samples a handful of these articles to convey the scope and flavor of the oeuvre, and the picture that emerges is of a writer who saw no boundary between the laboratory bench and the literary page.

He was equally inventive in another medium. Nakaya was a pioneer of educational documentary filmmaking in Japan, and he played an instrumental role in the formation of a major Japanese film studio. For a scientist of his generation, moving into cinema was an unusual and forward-looking choice, and it reflected the same instinct that powered his essays: that the public understanding of science required new forms, new audiences and new technologies of storytelling. His films brought the behavior of snow and ice to viewers who would never read a physics journal, extending the reach of his science far beyond the university.

Hamilton and Ohfuchi also situate Nakaya’s life in its Japanese cultural context and in the dramatic history of his era, which was shadowed by the Second World War. The war interrupted scientific collaboration across the Pacific and reshaped the institutions within which Nakaya worked, and the biography does not shy away from these difficulties. What survives the retelling is the coherence of the man’s project. Whether growing a snow crystal in a cloud chamber, drilling into Greenland ice with American colleagues, writing an essay about a Hawaiian expedition or producing a documentary film, Nakaya pursued a single goal: to make the physical world legible, and to make that legibility a shared public good. The new study, written for his 125th birthday year, introduces his life and achievements to an international audience that, until now, has known him mainly through a single elegant diagram and a handful of snowflakes made by hand.

Subject of Research: The life, snow crystal physics, glaciology and popular science writing of Japanese physicist Ukichiro Nakaya

Article Title: The Remarkable Scientist and Writer Ukichiro Nakaya and his "Black Moon" and "White Moon" Worlds

Article References: The Remarkable Scientist and Writer Ukichiro Nakaya and his "Black Moon" and "White Moon" Worlds. (n.d.). https://doi.org/10.5194/hgss-2026-12

Image Credits: AI Generated

DOI: 10.5194/hgss-2026-12

Keywords: Ukichiro Nakaya, snow crystals, Nakaya diagram, cloud chamber, glaciology, Greenland ice coring, popular science, science communication, history of science, Japan, climate change, documentary film