March 17: Thomas Maclear

Sir Thomas Maclear

March 17, 1794 – July 14, 1879

Thomas Maclear was an Irish-born South African astronomer who became Her Majesty's astronomer at the Cape of Good Hope.

Dr. Maclear had a keen interest in amateur astronomy, and would begin a long association with the Royal Astronomical Society, to which he would be named a Fellow. In 1833, when the post became vacant, he was named as Royal Astronomer at the Cape of Good Hope, and arrived there aboard the Tam O'Shanter with his wife and 5 daughters, to take up his new duties in 1834. He worked with John Herschel until 1834, performing a survey of the southern sky, and continued to perform important astronomical observations over several more decades. The Maclears and Herschels formed a close friendship, the wives drawn together by the unusual occupations of their husbands and the raising of their large families. Mary Maclear, like Margret Herschel, was a noted beauty and intelligent, though suffering from extreme deafness.

In 1750 Abbe Nicolas Louis de Lacaille had measured a triangulation arc northwards from Cape Town, to determine the shape of the earth and found that the curvature of the earth was less in southern latitudes than at corresponding northern ones. Sir George Everest visited the Cape in 1820 and visited the site of LaCailles measurements. From his experience in the Himalayas he believed that the presence of considerable mountain masses in the Cape could have caused false measurements to be made by LaCaille. Between 1841 and 1848 Maclear would be occupied in performing a geodesic survey for the purpose of recalculating the dimensions and shape of the Earth. He became close friends with David Livingstone, and they shared a common interest in the exploration of Africa. He performed many other useful scientific activities, including collecting meteorological, magnetic and tide data.

In 1861 his wife died. Two years later he was granted a pension, but did not retire from the observatory until 1870. He lived thereafter at Grey Villa, Mowbray. By 1876 he had lost his sight, and he died three years later in Cape Town, South Africa. He is buried next to his wife on the grounds of the Royal Observatory.

The Lunar crater Maclear is named in his honor.