Rambaut, Arthur Alcock (1859–1923), astronomer, was born 21 September 1859 in Waterford city, third son of the Rev. Edmund Francis Rambaut (BA, TCD), Church of Ireland clergyman and curate of Trinity, Waterford (later incumbent at Carysfort Church, Blackrock, Co. Dublin), and Madelene Rambaut (née Marlande), a first cousin. His interest in astronomy was no doubt influenced by his family's connection with the subject. Jean Rambaut, his great-grandfather, was born near Bordeaux, France, came to Dublin (1754), and married Marie Hautenville (1782). Two of their children married in a joint wedding ceremony (1821). The daughter, Elizabeth, married the Rev. Thomas Romney Robinson (qv), director of the Armagh observatory; and Arthur's grandfather, William Rambaut, married Maryanne Gibney of Dornstown Castle, Co. Meath. During Arthur's childhood his uncle William Hautenville Rambaut (1822–1911) was an assistant observer at Armagh observatory (1849–68).
He was educated at the Royal School, Armagh (1874–7) and at TCD, where he received a royal scholarship (1877) and later became a scholar of the college (1880). The following year he obtained his BA (1881) with a gold medal in mathematics and mathematical physics. After graduating he was appointed science master at his old school in Armagh but returned to Dublin (1882) as assistant to Sir Robert Ball (qv) at the Dublin University observatory at Dunsink, replacing John L. E. Dreyer (qv), who was appointed astronomer to the Armagh observatory. Rambaut continued in this position for eight years, and his regular observations with the Pisor and Martins Transit Circle are published in parts VI–VIII of the Astronomical observations and researches made at Dunsink and in the Monthly Notices of the Royal Astronomical Society's annual reports. He pioneered the use of photography at Dunsink observatory. Among the papers he wrote is a joint article in the RIA Transactions (1892) with Sir Robert Ball, on methods of measuring stellar photographs and of correcting the measures for errors. That same year (1892) Robert Ball was appointed Lowndean professor of astronomy at Cambridge, and Rambaut succeeded him as astronomer royal for Ireland and Andrews professor of astronomy (TCD). He continued his photographic work and wrote several more papers on this topic. Apart from his astronomical work he published a note on some Japanese clocks purchased for the Dublin Science and Art Museum (1889) in the RDS Scientific Proceedings. During this period in Dublin he received a M.Sc. (1887) and D.Sc. (1892) from TCD.
In 1897 he was appointed Radcliffe Observer (director of the observatory) at Oxford, where he continued the programme of observations initiated by his predecessors. He published a catalogue of the work (1906), consisting of 1,774 stars. In 1902 he had installed a large double refractor with a 24 in. (60 cm) photographic lens and 18 in. (45 cm) visual lens made by the Dublin firm of Howard Grubb (qv). This telescope was later transferred to the University of London observatory at Mill Hill, where it is still in operation. With this instrument he devoted much of the rest of his working life to investigating the Kapteyn method for determining mass stellar parallaxes and the proper motion of stars from photographic material. However, improved understanding of the systematic errors involved in measuring more than one star at a time rendered much of his exhaustive and painstaking parallax work of questionable value. He also made regular meteorological observations of temperature and rainfall which he communicated to the Thames Conservancy, for their regulation of the flow of the river.
He was elected a fellow of the Royal Astronomical Society (1893) and served on the council (1901–6, 1914–18), and was elected fellow of the Royal Society (1900). His observational work took him on two solar eclipse expeditions, to Vadsö, Norway (1896), and Placentia, Spain (1900).
Thoroughness, patience, and enthusiasm marked his working life. A genial family man, he married (2 January 1883) Emily, daughter of John Henry Longford of Blackrock; they had three sons, all born during Rambaut's time at Dunsink. Of delicate health, he became seriously ill in 1922 and died the following year, 14 October 1923. During the directorship of his successor, H. Knox-Shaw, the Radcliffe Observatory was moved to Pretoria, South Africa, during the 1930s and was later utilised by one of his Dunsink successors, Patrick Wayman (qv). Rambaut's letters to the Royal Astronomical Society are held in its library archive.