Back in May of this year we enjoyed beautiful weather while visiting the “Emerald Isle.” A couple of hours drive generally west of Dublin, Ireland is the town of Birr, and Birr Castle Demesne.
We took a guided tour inside the castle itself which is only offered during certain months of the year. The castle is not just an unoccupied museum piece but is the home of Brendan Parsons the 7th Earl of Rosse and his wife. The Parsons family have lived at Birr Castle since 1620. They celebrated their 400th anniversary last year.
We were able to walk and explore the extensive surrounding grounds or demesne (domain) which included award winning gardens, historic science center, I-LOFAR radio telescope, lake, river, waterfall, huge treehouse playground and the main attraction I was there to see, the The Great Telescope.
William Parsons the 3rd Earl of Rosse (1800-1867) had a serious interest in science, mathematics, engineering and most especially
astronomy and telescope making. He had built 18” and 36” telescopes using pretty much the same process to create the mirrors that resulted in the Leviathan. His passion for telescope building was refined and perfected by crafting the early instruments. This culminated with the completion in 1845, the very same year Texas became a state, of the massive 72″ Newtonian telescope which quickly became known as the “Leviathan of Parsonstown.”
The 54 ft. optical tube made of wood along with the mirror and mirror cell which prevented the huge disk of metal from deforming under its own weight came in at a whopping 12 tons. The huge effort to build the super structure and mammoth mirror was done onsite at Birr Castle.
The telescope had a six foot diameter finely polished, metal mirror made of speculum, an alloy mixture of 2/3’s copper and 1/3 tin, that was 5 inches thick and weighed 3-4 tons. The ability to fashion a glass mirror big enough for this telescope was simply not available at the time. Three huge crucibles each with their own furnace were used to heat up the alloy which took some 26 hours before they were all poured into the mold specially designed by the 3rd Earl himself. While the monster mirror solidified in just 20 minutes the annealing, grinding and polishing processes took months to complete. The grinding process alone took two months and was done with a steam powered machine.
Due to the brittleness of the alloy and it’s tendency to form cracks or break altogether, only two of five attempts to create the mirrors were successful. Two mirrors were necessary so that when one needed to be repolished, which was a frequent occurrence as speculum tarnished quickly, the other could be installed in it’s place, and thus premium observing time wasn’t lost. Additionally, another drawback to a speculum mirror was even freshly polished only 66% of the light that fell on the mirror would be reflected.
The telescope’s huge size required an equally huge structure to contain and point the beast toward the heavens. The 71 ft. long walls limited the telescope in azimuth but it had plenty of range in altitude. The walls were aligned parallel in a north-south direction and the earth’s rotation did the rest. To view an object one had to wait until the target was between the telescope’s walls in the sky. The observer would then have about 30 minutes of viewing time on either side of the meridian for that object.
The walls are 23 ft. apart with the optical tube between them and 40 ft. high. A system of axles, cables, weights and pulleys were used to move the scope to the desired position for observation. The observer would have to climb the structure to get to a movable platform at the top where the eyepiece could be accessed.
Along with being the largest telescope at the time, the Leviathan was also known as the most dangerous as well. With no electric motors to aid the process, a crew of men were necessary to manage the cabling system in the dark while the telescope was in use. Indeed it was a group effort to operate this telescope.
When the Great Telescope was first built in 1845 photography itself was just 20 years old. Astrophotography it’s safe to say was in its infancy, if it existed at all. Any attempt at taking pictures through the telescope would require super long exposures, much longer in fact than the telescope could provide given it’s lack of range in azimuth and completely manpowered tracking limitations. No, the only option at the time was to draw pictures of what was seen at the eyepiece. Making drawings at the eyepiece wasn’t anything new at that time but attempting it with the Leviathan? Try to image being almost four stories up on a open platform, dealing with wind and darkness trying to sketch what a galaxy looks like by the light of a lantern. But it was done, and some of the sketches were pretty remarkable. Speaking of photography William’s wife Mary was a noted photographer and took some of the first images of the telescope.
Once completed the 3rd Earl went directly to work and used the Great Telescope to confirm the spiral nature of the galaxies, specifically Nebula M51 as it was known at the time. William was sure of the object’s importance. He noted the spiral structure of the swirling arms and suggested that it had “dynamic” properties. Something many astronomers dismissed at the time. Although he didn’t know it at the time he’d just been the first to confirm that M51 was a galaxy. Nebula M51 became known as the Whirlpool Nebula shortly thereafter but it wasn’t until American astronomer Edwin Hubble observed Cepheid variable stars in the Andromeda Nebula in 1924 and mathematically confirmed the vast distances between us and some of these faint and fuzzy objects called nebulae.
When William Parsons died on Halloween in 1867 his son the 4th Earl, Laurence Parsons continued to operate the great telescope until 1890. Between 1874 and 1878 the Danish astronomer John Louis Emil Dreyer used the telescope to build on German-born British astronomer William Herschel’s “Catalogue of Nebulae and Clusters of Stars” (CN) which was first published in 1786 to create the “New General Catalogue” (NGC) in 1888. The NGC list contained over 7800 objects. Two supplementary “Index Catalogues” (IC) were also published. The NGC and IC catalogues are still widely used today.
The 4th Earl passed away in 1908 and by the time of World War I the great telescope had sat unused for a number of years. Much of the iron structure was collected and melted down for the war effort. One of the mirrors was saved and transported to the Science Museum in London. No one knows for sure what happened to the other mirror.
A revival of sorts happened in the 1970’s after Patrick Moore featured the Great Telescope at Birr in a TV program and this sparked talk of possibly restoring the telescope. It didn’t materialize but it did generate interest in the telescope, and the number of visitors coming to Birr Castle specifically to see the astronomical antique began to rise.
It wasn’t until the mid-1990s that a restoration effort gained traction. The current Earl of Rosse sought European help and governmental aid, and the huge task to reconstruct the Leviathan began. Between 1996 and 1997 the great telescope slowly came back to life. Budget constraints meant that a new mirror for the scope had to be done at a later time. Finally in 1999, one hundred plus years since the Leviathan was last used, a new mirror made of aluminum was installed and the restoration was complete.
The Great Telescope was an engineering marvel in its day and I can confirm it’s an impressive sight to see up close. Astronomers from all over the world came to Ireland to study the sky using the telescope. Along with the 3rd Earl’s study of the “spiral nature of nebulae” the great telescope provided the best detail visible of the Moon’s surface ever observed up until that time, distant planets were more accurately plotted and drawn and the temperature on the Moon was studied extensively by William’s son Laurence, the 4th Earl of Rosse.
The instrument reigned as the largest telescope in the world for over 70 years until it was surpassed in 1917 by the 100-inch Hooker Telescope at Mount Wilson Observatory in California. Appropriately, it was the 100 inch Hooker telescope that was next in line after the Leviathan to claim the “world’s largest” title, and the very same telescope Hubble had used in 1924 to gather the all important data on the Cepheid variable stars which extended our knowledge and understanding of the universe by quite literally millions of light years.
Clear skies!
Scott