Leviathan of Parsonstown, or Rosse six-foot telescope, is a historic reflecting telescope of 72 inches (1.83 m) aperture, which was the largest telescope in the world from 1845 until the construction of the 100-inch (2.5 m) Hooker Telescope in California in 1917. The Rosse six-foot telescope was built by William Parsons, 3rd Earl of Rosse on his estate, Birr Castle, at Parsonstown in Ireland.
Victorian picture of the "Leviathan of Parsonstown"
A 1:24 model of the telescope made by Parsons in 1844-45.
Reconstructed telescope seen from a distance
The Irish low-frequency array (I-LOFAR) radio telescope in the castle grounds.
A reflecting telescope is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a catoptric telescope.
Stratospheric Observatory for Infrared Astronomy
24-inch convertible Newtonian/Cassegrain reflecting telescope on display at the Franklin Institute
A replica of Newton's second reflecting telescope which was presented to the Royal Society in 1672.
The great telescope of Birr Castle, the Leviathan of Parsonstown. Modern day remnants of the mirror and support structure.