Birr Castle

The castle was built from 1620 and "gothicised" in the 19th century. It's the home of the seventh Earl of Rosse, Brendon Parsons (b 1936), with guided tours. But the main attraction is the grounds and gardens, of which the centrepiece is "The Leviathan of Parsonstown", the great telescope completed in 1845. It's a 72-inch reflector: the third Earl devised methods of grinding a mirror weighing three tons, and it was the world's largest telescope until 1917. It was mounted on an iron arc, giving it a wide range of altitude, but limited azimuth (side-to-side) so objects could only stay in view for an hour. The telescope was used to 1890 then succumbed to disuse, but was restored in the 1990s. In 2017 a low-frequency radio telescope was installed in the castle grounds.