This 19th-Century Telescope Offered Early Hints of Far Away Galaxies

In the early 1840s, a mysterious structure began looming over trees and fields near the Irish village of Parsonstown. By 1845, the tower housed the most advanced scientific instrument in the world: a 56-foot-long reflecting telescope with an unprecedented 6-foot diameter. It was contained within a rotating wooden framework that weighed about 15 tons and stood more than 50 feet high.

“The construction… required skilled carpenters, masons, large metal furnaces and metallurgists to cast the speculum mirror, chains, pulleys and secondary mirrors,” explains Alicia Parsons, daughter of the seventh Earl of Rosse and great-great-great-granddaughter of William Parsons, the third Earl of Rosse, who had the giant instrument built on the grounds of nearby Birr Castle. “The telescope became a source of pride for the community, and it was affectionately nicknamed ‘The Leviathan of Parsonstown’ by locals.”

The telescope was at the cutting edge of technology. William Parsons had developed new methods of using speculum—an alloy of copper and tin—and built machines near the Leviathan site to grind and polish the brittle metal into two huge mirrors for his new telescope. (Speculum can be highly polished but tarnishes quickly.)

Until the Leviathan was built, the largest telescope was a 49.5-inch-wide reflector (just over four feet across) built in England by 18^th-century astronomer William Herschel. Herschel discovered two moons of Saturn with that telescope, but it was difficult to use. The Leviathan was designed to overcome its limits.

William Parsons’ main goal was to use the Leviathan to investigate mysterious “nebulae” recorded by the 18^th-century French astronomer Charles Messier and William Herschel’s son, John Herschel, who was a prominent astronomer in his own right and had continued his father’s work. These fuzzy-looking objects (nebula is Latin for “cloud”) were at the limits of the Herschel telescope’s resolution.

In 1845, Parsons used the Leviathan to determine that one nebula had a spiral structure. He called it the “Whirlpool Nebula,” but it has since been recognized as the Whirlpool Galaxy, located roughly 30 million light-years from the Milky Way. Science at the time had no knowledge of galaxies, however, so Parsons did not truly realize what he had seen.

Alicia Parsons notes that every detail of the Leviathan had to be designed and built from first principles. William Parsons experimented with the mix of speculum metal used to make the mirrors, as he looked for an alloy that would give almost perfect reflections while not deforming under stress or corroding too quickly in the often rainy Irish weather. He also invented a special mold to cast the mirrors from molten speculum and built special ovens so they could cool for several days afterward without cracking. The mirrors were then molded into the correct curvature, polished and transported on a trolley on rails that led to the Leviathan site.

The Leviathan’s massive rotating wooden framework was housed within heavy brick walls designed to bear its weight. It could rotate 10 degrees from east to west and 110 degrees from north to south. “As stars travel east to west through the sky at night, this allowed him to follow a star or nebula for an hour,” Alicia Parsons says.

Finally, an eyepiece was added to the giant instrument, and moving galleries were attached near the top of the telescope to let William Parsons peer through it. “All [this] required a series of weights, counterweights and pulleys, and sometimes underground tunnels, to make sure the telescope operated smoothly,” Alicia Parsons says.

The Leviathan was a great success. Its observations showed that many of Herschel’s nebulas were actually star clusters, and several were later determined to be distant galaxies. Parsons also carried out important observations of the moon, Mars and Jupiter. But the speculum mirrors corroded quickly and needed frequent removal and repolishing. And Ireland’s frequently cloudy skies meant it could only be used for about 100 nights every year.

William Parsons’ son Lawrence Parsons, fourth Earl of Rosse, continued his father’s astronomical work until the early 20th century. The giant telescope then fell into disuse afterward and was dismantled. By 1917, the even larger 100-inch Hooker Telescope had been built at Mount Wilson in California. In the 1920s it was used by astronomer Edwin Hubble to prove that Andromeda was a separate galaxy—one of the first ever discovered.

In the mid-1990s, historians and engineers built a working replica of the Leviathan at the original site. It still stands today, though the replica telescope inside it—now with an aluminum mirror—is no longer used for observations. The reconstruction effort included research into the original 1840s design, and it cost more than $1 million to build. (The cost of the original Leviathan cannot be calculated, but it’s estimated to have been the modern equivalent of several million dollars.)

Birr Castle’s giant telescope replica and newly built science center are now major tourist attractions. But the Leviathan was not the last astronomical project there. In 2017, a field of radio antennas known as I-LOFAR was erected nearby to conduct observations for the international LOFAR consortium of 52 radio telescopes—a world-spanning network that combines to form one of the most sensitive radio telescopes ever.

“It’s a phenomenal connection,” says Trinity College Dublin astronomer and astrophysicist Peter Gallagher, who directs the project. “The Leviathan was the biggest optical telescope in the world in the 1840s, and over 150 years later, the I-LOFAR instrument is part of the largest radio telescope in the world.”