Telescopes from the Ground Up

A telescope big enough to be named after a monster

The Leviathan of Parsonstown: That’s what the public named the telescope built in 1845 by Irish nobleman William Parsons, the third Earl of Rosse.

A leviathan is a giant sea monster. With a 72-inch metal mirror weighing 4 tons and a tube 54 feet long, it’s easy to see why people were so impressed by the reflector. The telescope was the high point of Lord Rosse’s astronomical adventures.

Only the best

Rosse had decided that he wanted to build the world’s largest telescope. But to do that, he first needed to build the biggest mirrors. William Herschel hadn’t left behind any records of his mirror-making methods, so Rosse had to start almost from scratch.

Over 17 years, he managed to make a 15-inch (38-centimeter), 24-inch (61-centimeter) and finally a 36-inch-diameter (91-centimeter) mirror. Technology improvements, such as grinding tools powered by a small steam engine, meant he had an easier time crafting the mirrors than Herschel had experienced.

Get to the root of it

Rosse placed the 36-inch mirror in a Newtonian reflector. But he wasn’t satisfied yet. In 1842, he began to work on a 72-inch mirror. It took five tries before he created a mirror that could be used, and 3 years to build the actual telescope.

Click here to see all avaliable eras.
Show More
Early Reflectors
Map of Birr Castle, Parsonstown, UK, where the Leviathan reflector built by Lord Rosse was located.
See major discoveries of this telescope.
Image of the Leviathan of Parsonstown, a large reflector built by Lord Rosse.Enlarge picture
The Leviathan of Parsonstown
Year completed: 1845
Telescope type: Reflector
Light collector: Metal mirror
Mirror diameter: 72 inches
(1.8 m)
Light observed: Visible
Discovery Highlights:
  • First telescope to view the spiral structure of the object then known only as M51. M51 would later be known as the Whirlpool Galaxy.
Read more…