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In the 1800s, William Parsons built a telescope larger than any in the world: The Leviathan of Parsonstown. This landmark in science history helped solve the mystery of just what a nebula could be.

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About 200 years ago, astronomers had a bit of a debate on their hands. In the late 1700s, astronomer Charles Messier had put together a list of more than a hundred objects that appeared fuzzy—or nebulous—in his telescope.

At the time, it was the world’s best catalog of these so-called nebulas. And as Messier’s discoveries piled up, astronomers fiercely debated a simple question: What were they? Some thought these objects were hundreds or thousands of stars too small to be clearly resolved.

Others thought their strange glow came from a gas-like substance floating in space. The only way to figure it out was to build a bigger telescope. And that is where the Leviathan of Parsonstown came in: a telescope larger than any in the world, built into what became basically a small fortress.

The Leviathan was constructed on the grounds of Birr Castle in Ireland, home to William Parsons. A mathematician by training,. Parsons returned to his estate in the 1830s after a successful career in politics.

And there, he used his new free time to build and study several telescopes. But his legacy really began in 1841, when he took over as the Earl of Rosse from his father. The new title gave him the resources to put some of his engineering ideas to the test with a telescope of unprecedented size; one big enough to finally identify Messier’s nebulas.

Except, no matter how many fancy titles you had, it was incredibly difficult. At the time, the world’s largest telescope had a mirror 48 inches in diameter; around 1.2 meters. Parsons wanted to build one with a diameter of 72 inches, or 1.8 meters, which would collect more than twice as much light.

But adding those extra 60 centimeters was much easier said than done. Today, telescope mirrors are mostly made of glass, with a thin coating of a metal like aluminum to provide the reflective part. The glass creates the shape, and the aluminum adds the shine, resulting in a mirror that is relatively light and resistant to tarnishing.

But in the 1800s, mirrors for telescopes were cast out of a bronze alloy called speculum. Speculum was about as reflective as materials got back then, and was relatively easy to work with. But, to make a mirror almost two meters in diameter required four tons of metal to be melted and then slowly cooled, over a period that would stretch from weeks up to four months.

Also, to focus the light well, the rough mirror, called a blank, needed to be shaped into a virtually perfect parabolic curve. Traditionally, this was done by hand. But in the spirit of the Industrial Revolution, Parsons developed a steam-powered machine that rotated the blank underneath an iron polishing tool.

Still, polishing the blank required two months of painstaking work, and it took him and his laborers five tries to successfully cast and polish such a massive mirror. And then, they had to make another one. See, speculum was highly reflective, but it also tarnished really quickly, so keeping the telescope in operation required alternating between two mirrors.

And that was only one part of the design. At the same time, his team was also constructing a wooden tube for the mirror to be mounted in, which extended nearly 18 meters. The tube was attached to the ground at one end and could be pointed up and down using a pulley system that weighed 150 tons; so much that everything was supported by two massive stone walls.

And you are starting to realize now why they called it the Leviathan. That stone fortress did the job, but it also left the telescope with one huge flaw:. While it could be pointed up or down at basically any angle, the walls prevented it from turning left or right.

So, looking at a specific spot in the sky meant waiting until the Earth had rotated just right for the object to come into view. And then of course, they would stop the Earth from moving so they could look at it- no, the Earth is always moving, so keeping an object in view required a team of five people to manipulate the pulleys. Being the observer also was no picnic.

Photography was in its infancy, so observations with the Leviathan were made by standing in a small cage at the top end of the tube and peering through an eyepiece. Then, you had to just sketch whatever you saw on a nearby easel. Now this all sounds a little bit primitive, but apparently,.

Parsons and his team were decent artists, because those sketches helped answer the question of nebulas and revolutionized astronomy. Within a month of the Leviathan’s completion in 1845,. Parsons shared a sketch of the object known as Messier 51.

It showed a collection of individual stars arranged in a spiral structure. Parsons was convinced that these stars moved together as one cohesive object. And he was right!

He didn’t know it, but this was the first-ever detailed observation of another galaxy. And it would not be his last. In time, Parsons, his son, and their assistants would identify 57 so-called spiral nebulas, of which 48 we know now are galaxies.

And at the same time, he also definitively proved that other nebulas weren’t made of stars, but of brightly-glowing gas. So a thing that is extremely unusual in science happened: two groups of people disagreed about what something was, and they were both right. These days, you can still visit the telescope, but its days of serious research are long gone.

The Leviathan remained in use into the 1880s and was eclipsed in size in 1917 by the 2.5-meter Hooker telescope at Mount Wilson Observatory in Los Angeles. But it is still a landmark in science history. I hope to be able to go visit it one day.

It helped to settle a major debate, and started to reveal that the universe is far bigger and more interesting than just what’s in our galaxy. It was also an incredible engineering achievement, from the artistry needed to make the mirrors to the stone walls that held it all together. So if you ever find yourself near Birr Castle, stop by and say hello to one of the greats, tucked away in Ireland.

No matter where you are, though, you can still celebrate this telescope with our Pin of the Month! Like the name says, we release a new one of these every month, and February’s pin is the Leviathan of Parsonstown. It was designed by one of our SciShow team members, and will be only available until the end of the month.

In March, we will be back with a new design. If you want one, head on over to [♪ OUTRO].