Don Mathewson was Stromlo’s first Australian Director since its founder Walter Geoffrey Duffield. Mathewson began his career in radio astronomy at the CSIRO in 1955, before moving to Manchester to complete his PhD. In 1974, Mathewson made a significant discovery – ‘a huge arc of gas 120 degrees wide (corresponding to 600 000 light years), going across the sky from the Magellanic Cloud.’ Mathewson named it the Magellanic Stream – astronomers are still unsure of the origins of these interstellar clouds of gas.

Mathewson was one of the Professorial Fellows at the ANU when Eggen resigned, and was appointed Acting Director. Once confirmed as Director in 1979, Mathewson focussed the Research School’s studies on the evolution of stars and the determination of the Hubble Constant – a unit of measurement to depict the expansion of the Universe. He continued to build the academic credentials of the Observatory Astronomer Dr. Ragbir Bathal described him as “very Australian, energetic, approachable, decisive, a great bustler-around . . . Don was largely responsible for taking Australia into the Space Age.”

In the final months of his directorship, Mathewson invited parliamentarians, embassy and industry leaders to the Observatory to view the close approach of Comet Halley. Most guests expected to view the comet through the 74-inch telescope, but its small field of view meant that a pair of binoculars was more appropriate. Frame & Faulkner wrote that “it took a great deal of tact to persuade some VIPs that they were not being fobbed off with a second rate experience.” On the 7^th April 1986, Prime Minister Bob Hawke was one of the attendees. This special audience was treated to a live video-link of the comet from the 2.3 metre reflector in Siding Spring. There was scepticism that this image hadn’t been pre-recorded, and one of the guests challenged Mathewson to focus the telescope on something else. Frame & Faulkner recounted the tense moments: “Saturn’s familiar ringed spectacle appeared, to the great relief of all of the Stromlo staff. An enthusiastic cheer rang out – they were convinced! Bob Hawke was heard to remark what his sentence on the Director would have been had Saturn not appeared: ‘Off with his head!’” Mathewson completed his directorship in 1986 and returned to his research of spiral galaxies.