Sidney Charles Bartholemew "Ben" Gascoigne AO (11 November 1915 – 25 March 2010) was a New Zealand-born optical astronomer and expert in photometry who played a leading role in the design and commissioning of Australia's largest optical telescope, the Anglo-Australian Telescope, which for a time was one of the world's most important astronomical facilities.

Born in Napier, New Zealand, Gascoigne trained in Auckland and at the University of Bristol, before moving to Australia during World War II to work at the Commonwealth Solar Observatory at Mount Stromlo in Canberra.

They also found that star formation in the Magellanic Clouds had occurred more recently than in the Milky Way; this overturned the prevailing view that both had evolved in parallel.

When the British and Australian governments agreed to jointly build the Anglo-Australian Telescope at Siding Spring, Gascoigne was involved from its initial conception and throughout its lengthy commissioning, taking its first photograph.

[3] He completed both a Bachelor's degree and a Master's qualification in science, securing Honours in both mathematics and physics, finishing his studies in 1937.

[2] During his thesis studies at Bristol, Gascoigne developed a diffraction theory of the Foucault test that is used for evaluating the shape of large telescope mirrors.

[1][2][4] Returning to a job in the physics department at Auckland, Gascoigne worked on military optics, developing gun sights and rangefinders,[1] although he did not remain there for long.

Gascoigne began to work in the nascent field of photoelectric photometry, using electrical devices to measure the brightness of stars more accurately than had been possible using photographic techniques.

The research produced remarkable results: "it meant that the Magellanic Clouds were twice as far away as was previously thought, and if then the baseline is twice as long, the size of the universe is doubled.

[5] Like many Observatory personnel, the Gascoignes lived in a staff residence on Mount Stromlo, which was a long difficult trip away from Canberra.

[17] Also in 1957, the Mount Stromlo team began searching for a new field observatory site, due to the increased light pollution from Canberra's growth.

Gascoigne, looking for a new research project and keen to use the new telescope, took up the study of globular clusters, compact groups of tens of thousands of ancient stars of similar age.

Gascoigne determined that the clusters in the Magellanic Clouds were both young and old, and had quite different characteristics to those in the Milky Way: this information was important for modelling the evolution of galaxies.

[23] In 1963, Gascoigne developed a device, known as an optical corrector plate, which allowed wide field photography on the new 40-inch telescope at Siding Spring.

[29] Gascoigne was then given a significant opportunity that became the focus of the remainder of his paid academic career: to help establish one of the world's largest optical telescopes, at Siding Spring.

In the early 1960s, the Australian and British governments proposed a partnership to build a joint optical telescope facility, and Gascoigne was among the experts involved.

[30] Former Mount Stromlo director and now head of the Greenwich observatory, Richard Woolley, was prominent in supporting the project from the British end.

[37] Gascoigne was one of only a few Stromlo employees who ended up working on the AAT for an extended period during its establishment phase:[note 2] the Anglo-Australian Observatory chose to offer short-term positions rather than academic tenure like that at the ANU.

[39] Gascoigne was so pleased with the quality of the optics that he said he wanted a number describing the hyperboloid shape of the mirror (1.1717) engraved on his headstone.

[40] The site quickly became one of the world's most important astronomical observatories[41] and was for many years home to world-leading astrophotographer David Malin.

"[1] It was during the period of Gascoigne's association with the Anglo-Australian telescope that he and his wife commissioned architect Theo Bischoff to design a house for them, which was planned and constructed between 1967 and 1969.

Gascoigne decided to return to the Australian National University in Canberra; he retired a few years later in 1980, and supported Rosalie in her work.

"[1] Rosalie Gascoigne's artistic career came late – she was almost 60 when she held her first solo shows – and her rise was "meteoric"; five public galleries purchased works from her early exhibitions.

[1][5] In 2008, Gascoigne donated Rosalie's final major work, a ten-panel installation titled Earth (1999), to the National Gallery of Australia.

English astronomer and writer Sir Fred Hoyle, at one time the Chairman of the AAT, gave Gascoigne considerable credit for the telescope's success,[58] and astronomer Harry Minnett likewise credited him, together with Roderick Oliver Redman, for the telescope's extremely good optics.