The Observatory on University Gardens was planned in 1938 and opened on 17 April, 1939 by Sir Arthur Eddington, the distinguished astrophysicist and early proponent of Albert Einstein’s theory of relativity. The University decided to replace the old Horselethill Road Observatory because it was in a poor state of repair and because the encroaching city had made serious observation impractical. William Marshall Smart, the new Professor of Astronomy, recognised the need for new facilities and a new approach to astronomy at Glasgow. In a pragmatic and politically astute move, he re-focused the department on teaching and theoretical research and largely abandoned advanced practical research. The University received an offer from the Trustees of Notre Dame Convent to buy the Observatory building in 1937. At the same time, the University purchased a plot of vacant ground at the west end of University Gardens.
The new Observatory, planned in 1938, was a relatively small building designed by Stewart&Paterson. John Stewart had been an apprentice in the Burnet, Son & Campbell office in the early 1890s, and George Andrew Paterson had been apprenticed to Honeyman & Keppie in the mid-1890s. Stewart & Paterson drew up plans for a new single-storey building. It was a simple range with a rear wing and a mildly Art Deco doorway. The structure was capable of upward expansion if necessary. Inside there was a large library, an instrument room, and rooms for Professor Smart and his assistant, T.R. Tannahill. The 7-inch refractor telescope and transit circle (instrument for measuring the precise position of stars) houses were built separately at the top of the bank behind the Observatory.
After the Second World War the department flourished in its new location under Smart and his successor, Peter Sweet, to the extent that conditions were again cramped by the early 1960s. At this time planning began for improved staff accommodation and undergraduate practical teaching equipment and facilities at the Garscube Estate. The University Gardens Observatory was demolished in 1966 to allow for the construction of the Queen Margaret Union. The department occupied temporary accommodation in Ashton Road from 1964 until a new observatory was opened at Garscube in March 1969.