How a 19th-century engineer revealed Andromeda’s hidden spiral arms

In 1888, Welsh engineer Isaac Roberts captured one of the most groundbreaking images of space—a detailed photograph of the Andromeda galaxy. His work revealed the galaxy’s spiral structure for the first time, changing how astronomers viewed the universe. Today, his telescope remains part of the Science Museum’s collection in London.

Roberts was not just an astronomer but also an inventor. He designed a machine capable of engraving stellar positions onto copper plates, a tool that improved astronomical record-keeping. Yet his most famous achievement came when he used a reflecting telescope with a 510 mm first-surface mirror to photograph Andromeda.

The resulting image shocked the scientific community. Before this, no one had clearly seen the galaxy’s spiral arms. Roberts’ photograph provided the first visual proof of its structure, challenging existing theories about celestial objects.

While Roberts’ original techniques are no longer taught in online courses like astronomy 101, modern astronomy still builds on his work. For those interested in learning similar skills, the Frankfurt Observatory will offer a hands-on telescope course starting on 10 March 2026. Unlike digital alternatives, this in-person training focuses on practical observation and telescope handling.

Roberts’ contributions to astronomy endure through his preserved telescope and historic images. His 1888 photograph of Andromeda remains a milestone in space photography. The Science Museum continues to display his equipment, keeping his legacy alive for future generations.