The Great Telescope, the Leviathan of Parsonstown
About
A 72-inch reflecting telescope, 16.5 metres of focal length, slung between two masonry walls in the middle of the demesne. William Parsons, Third Earl of Rosse, cast six speculum mirrors between 1842 and 1845 to get two usable ones, and finished the mounting in 1845. The UNESCO and IAU Portal to the Heritage of Astronomy records it as the largest telescope in the world from 1845 until the 100-inch Hooker Telescope was built at Mount Wilson in California in 1917; Birr Castle's own account of the instrument dates the record 1845 to 1914, the year the original speculum went to the Science Museum in London. With it Rosse first drew the spiral structure of M51, later called the Whirlpool Galaxy, and astronomers came to Birr from across Europe because there was nowhere else with an instrument this size. It was restored in the late 1990s with a new modern mirror in 1999 and the estate says it was last used in the early 2000s. It stands outdoors and is free to walk up to once you are inside the demesne.
Photos
Highlights
- ✓72-inch speculum mirror, 16.5m focal length
- ✓Where the spiral structure of M51 was first drawn, in 1845
- ✓Restored in the late 1990s with a new mirror in 1999
- ✓The I-LOFAR radio telescope is in the same parkland
Tips
- →Go to the Science Centre first: the galleries explain how the mirror was cast and the tube was built in the castle workshops, and the telescope makes more sense afterwards.
- →The original 1845 speculum mirror is not here. It has been in the Science Museum in London since 1914.
- →I-LOFAR, the radio telescope run by Trinity College Dublin, is on the same site and visible from the demesne paths.
Best Season
More Attraction Activities
Birr Castle Demesne
120 acres of parkland, gardens, rivers and a working science site behind the wall on Rosse Row. The demesne is the visitor offer; the castle is a private home.
Ireland's Historic Science Centre
Seven galleries on the Parsons family's telescopes, early photography and engineering, including the oldest intact darkroom in the world.
Birr Theatre and Arts Centre
The Oxmantown Hall of 1888, opened in January 1889, restored by the town and reopened in 2000 as a 220-seat theatre and the hub of Birr's festivals.