David Vyvyan Thomas was born in Swansea in 1930, the elder son of two teachers. He became interested in astronomy at a very early age and quickly realised he wanted to be an astronomer. With this goal in mind, he studied A-Level Maths, Physics and Chemistry at Swansea Grammar School (1941-1948). Encouraged by the formation of the Swansea Astronomical Society in 1948, he went on to study Astronomy at Glasgow University (1948-1952), gaining a 2.1, during which time he spent the summer vacation of 1951 at Cambridge Observatory. Following graduation, he briefly taught Maths and Technical Drawing at a grammar school in London in 1953, before taking up a PhD at Pembroke College, Cambridge. His thesis focused on the determination of the temperature of the solar chromosphere (4500 degrees) from measurements of CN lines in Redman’s 1952 eclipse spectrum. He married Glasgow graduate Toni Brown on 15 September 1956. They had two daughters and a son, the second daughter being born in Cape Town while he was on secondment at the RO Cape. There are four grandchildren. His wife died in 2013.

Thomas joined the RGO’s Solar Department at Herstmonceux Castle in November 1956. His first major tasks were observing and measuring sunspots and flares, observing double stars with the 28" Refractor (1957-59), and working for the Astronomer Royal on the analysis of three-colour photometry. In 1958, he moved to the Meridian Department where his work involved determining proper motions from Airy Transit Circle observations alone (a programme which was later abandoned). He also developed a program for the ICT 1201 computer for Least Squares solutions in up to seven variables. This was subsequently used, inter alia, to determine orbital elements of spectroscopic binaries observed by D.H. Evans at RO Cape.

From 1960-1964 he was based at the Time Department, where he took over the management of the Photographic Zenith Tube and Astrolabe observing programmes from C.A. Murray. His work involved the monthly publication of time and latitude results, publishing papers on the reduction and analysis of PZT observations, and an analysis of the design of observing programmes such as those of the PZT and Astrolabe. He published the collected Astrolabe observations in 1965, followed in 1971 by the publication of the analysis and resulting catalogue corrections to places of 250 stars.

In 1964, the Astrolabe was taken out of service and transferred by Thomas to RO Cape at the request of HM Astronomer (R.H. Stoy). As a result, Thomas spent 1964-1967 on overseas duty at RO Cape, where he set up and ran a programme of astrolabe observations, continuing for two years after his return to Herstmonceux. During this time, he regularly published time and latitude results in MNASSA. Over the next ten years, he devoted what time he could spare from his main duties to the analysis and derivation of catalogue corrections for over 1000 stars, which he published in 1979. During his time at the RO Cape, Thomas also investigated the defective performance of the 40" Elizabeth reflector-corrector and in 1966, spent three months at Pretoria taking part in observing programmes on the Radcliff 74" reflector.

He was promoted to Principal Scientific Officer (PSO) in 1965 and on his return to RO Herstmonceux in 1967, moved to the Astrometry Department, where he worked until 1973, mainly on the 26" parallax programme. In 1967, he was elected Chairman of the RGO section of the SRC branch of the IPCS, which involved meetings with RGO management on staff matters and representation of the RGO at SRC level. From 1973 to 1979, he was Assistant to the Director (SPSO), during which time he essentially reorganised and ran the Observatory while the Director concentrated on directing the scientific programme and high-level contacts. He also chaired the Organising Committee for the RGO contribution to RO tercentenary.

Thomas left the RGO in 1979 for senior positions at S(E)RC headquarters in Swindon, retiring in 1990. Moving to Sidmouth in 1997, he was active in the Norman Lockyer Observatory until his move to Edinburgh in 2004.