Clerke, Agnes Mary (1842–1907), historian of astronomy and scientific writer, was born 10 February 1842 in Skibbereen, Co. Cork, second child and younger daughter of John William Clerke, manager of the Provincial Bank, Bridge St., and his wife Catherine Mary, youngest sister of the politician and lawyer Rickard Deasy (qv). Agnes and her sister Ellen were educated entirely at home by their intellectual parents. Their father, a graduate of TCD, was well versed in the sciences, and maintained a telescope with which he provided a time-service for the town of Skibbereen. Instructed by him, Agnes covered a substantial course of basic astronomy while still a young girl. Later, her brother Aubrey, who excelled in mathematics at university, coached her in more advanced topics.
In 1861 the Clerkes moved to Dublin when the father became court registrar to his brother-in-law. After some years' residence there the sisters spent ten years in Italy, principally in Florence, where they continued their studies privately, becoming fluent linguists. Agnes's particular interest at that time was the science of the renaissance. In 1877 the entire family settled in London, where Agnes, at the age of 35, commenced her career as a professional writer with twice-yearly contributions, mainly with an astronomical flavour, to the erudite Edinburgh Review. Her excellent scientific biographies in the Encyclopaedia Britannica, begun in 1879, including those on Galileo and Laplace, brought her name to the notice of the educated public.
She now set about studying the ‘new astronomy’ or astrophysics, a relatively new branch of astronomy, working alone in the library of the British Museum. This resulted in the work for which she is best known and which remains a classic of the history of science, A popular history of astronomy during the nineteenth century (1885). The History, labelled ‘popular’ to denote that it was a non-mathematical treatment, was an immediate success for its usefulness to the professional astronomer and its appeal to the general reader. It went into three editions in its author's lifetime.
The book brought her a wide circle of admirers including the astronomer and writer Joseph Norman (later Sir Norman) Lockyer, founder of the journal Nature, and William (later Sir William) Huggins and his Irish wife and collaborator Margaret, who became a close personal friend. Among her correspondents were Edward Holden, first director of Lick Observatory in California, E. C. Pickering of Harvard, and leading astronomers in the United States and Europe whose work she reported in British and American journals, principally Nature, The Observatory, Knowledge, and Astronomy and Astro-Physics. So reliable, thoughtful, and wide-reaching were her analyses that she became a revered authority and an influential propagandist, especially in the rapidly expanding field of astronomical spectroscopy. Her practical experience, however, was limited to three months in 1888 spent at the Royal Observatory, Cape of Good Hope, as the guest of its director David (later Sir David) Gill, where she made actual astronomical observations of stellar spectra which were published. She declined an opportunity of employment at the Royal Observatory at Greenwich, preferring to devote her life to writing. Her second important book, The system of the stars (1890) championed the one-system universe, the favoured model at that time. In this system all objects are held to belong to one finite agglomeration, as opposed to the rival model of multiple island universes filling infinite space. The one-system model as defined by Clerke was widely accepted till the discovery of the expanding universe in the 1920s.
Clerke had close associations with the Royal Institution, where she was an assiduous attendant at its scientific lectures. In 1893 she received the Institution's distinguished Actonian prize, awarded septennially for work demonstrating the ‘beneficence of the Almighty’ in science. She was commissioned to write an account of Sir James Dewar's experiments in the liquefaction of gases for the Hodgkins Trust (Low temperature research at the Royal Institution 1893–1900 (1901)). She was elected a Member of the Royal Institution in 1902.
In 1903 Clerke published her third major book, Problems in astrophysics, which attempted to identify unresolved questions and to suggest projects that might solve them. This book was deemed her most impressive by her contemporaries, though, as the problems of the day gave way to later quite different ones, it has not proved as enduring as her History. Shortly after it appeared, Clerke was made an honorary member of the all-male Royal Astronomical Society. Problems in astrophysics was followed by Modern cosmogonies (1905), a popular historical account of the various models of the world leading to contemporary ideas in physics and biology. It was noteworthy for its philosophical tone, and for its revelation of the author's antipathy to the agnostic view of science.
Clerke was a core contributor to the original volumes of the Dictionary of National Biography, providing 150 entries, to which may be added some thirty biographies of astronomers in Encyclopaedia Britannica (eleventh ed., 1911). Among her subjects were the Herschels – William, Caroline, and John – whose lives she also published in book form (The Herschels and modern astronomy (1895)). Her writings on non-scientific subjects include some charming essays on references to everyday life in Homer's poetry, Familiar studies in Homer (1892). Clerke's sister, Ellen Mary (qv) (1841–1906), pursued her own career as a poet, writer and journalist, principally in the London catholic press.
Agnes Clerke died at her home in Redcliffe Square on 20 January 1907. A plaque commemorating her and her sister marks their birthplace in Skibbereen. Agnes has also been commemorated by the naming of a crater on the moon.