Maclear, Sir Thomas (1794–1879), surgeon and astronomer, was born 17 March 1794 at Newtownstewart, Co. Tyrone, eldest son of the Rev. James Thomas Maclear. His mother's maiden name was Magrath. His father intended him to enter the church but, refusing to embark on a clerical career, he left home and moved to England (1808). He studied medicine at Guy's and St Thomas's Hospitals, and in 1815 was made a member of the Royal College of Surgeons in London. In the same year he joined the staff of the Bedford Infirmary, and while there he made the acquaintance of Adm. William Henry Smyth, who (besides being a naval hero) was a hydrographer, writer, and later president of the Royal Astronomical Society. Maclear used this opportunity to study mathematics and astronomy and his friendship with Smyth ultimately changed the course of his career.
In 1823 he moved to Biggleswade, Bedfordshire, where he established a medical practice in partnership with his uncle. He set up a small observatory in his garden and engaged in a series of astronomical observations. A member of the Royal Astronomical Society from 1828, he carried out a series of calculations to determine the occulations of Aldebaran, and in 1829 the society loaned him the Wollaston telescope so that he could confirm his findings. Elected a fellow of the Royal Society (1831), he was appointed royal astronomer at the Cape of Good Hope (1833), arriving in South Africa in January 1834. In this capacity he worked in cooperation with the Royal Observatory in Greenwich, and while in South Africa became a close associate of Sir John Herschel. In 1837 he began a series of observations that resulted in the remeasurement and extension of the meridian arc of Lacaille; these calculations had implications for later surveys of the African continent. He observed the Alpha and Beta Centauri and confirmed the measurements of Thomas Henderson's parallax. In 1860 he was knighted in recognition of his astronomical work. Comets and double stars were an area of special interest to him and he carried out a series of prolonged observations of Halley's and Donati's comets. In 1862 he finished a series of observations of Mars; his calculations were used by later astronomers to determine the earth's distance from the sun.
Throughout his time in the Cape he published the results of his observations, and these mostly appeared in the Memoirs and Monthly Notices of the Royal Astronomical Society. His observations of all the southern stars, carried out between 1849 and 1852, appeared in successive editions of the Cape Catalogue. He also published The verification and extension of Lacaille's arc of the meridian at the Cape of Good Hope (2 vols, London, 1866). He was awarded the Lalande prize (1867) for his work on Lacaille's arc, and in 1869 was awarded the Royal Medal. A member of numerous learned societies, he was a corresponding member of the Institute of France (1863). He was also elected to the Imperial Geographical Institution in Vienna and the Academy of Sciences in Palermo. A man of ceaseless activity, he failed to publish many of his calculations.
Alongside his astronomical work, he carried out a series of magnetic, tidal, and meteorological observations. He was keenly interested in the improvement of the Cape Colony, sat on the weights and measures committee, and also promoted sanitary improvements. In 1860 he established a facility to transmit time signals from Port Elizabeth and Simonstown. He was involved in the building of lighthouses and, interested in the exploration of Africa, was a friend of both Livingstone and Stanley. After the death of his wife (1861), he began to suffer increasingly from ill-health, retiring from his work at the observatory in 1870. He moved to Grey Villa, Mowbray, near Cape Town, but by 1876 was totally blind. Cared for by members of his family, he remained active in the civic affairs of the colony. He died on 14 July 1879 and was buried in the grounds of the observatory, alongside his wife. On 17 July 1879 the town assembly passed a resolution of thanks in which his services to the colony were praised. The town of Maclear in the Eastern Cape, South Africa, and a crater on the Moon were later named in his honour.
He married (1825) Mary (d.1861), daughter of Theed Pearse, clerk of the peace for Bedford. They had four sons and six daughters.