on top of the western wall are used, which can be moved across the wall to follow the telescope in azimuth. Operation The purpose of the telescope was to re-visit the nebulae in the catalogues of Charles Messier and John Herschel. These catalogues list star clusters as well as nebulae, and the question was whether the latter were merely unresolved star clusters or genuinely nebulous regions of space. It resolved into stars unclear areas which might be the first galaxies to be identified as such. Parsons discovered that several nebulae had a spiral structure, suggesting "dynamical laws". The most notable spiral nebula observed by Parsons was Messier 51, which he resolved into stars. After William Parsons (the 3rd Earl of Rosse) died in 1867, the 4th Earl (Laurence Parsons) continued to operate the six-foot telescope. From 1874 to 1878, J. L. E. Dreyer worked with the telescope and began the compilation of his New General Catalogue of Nebulae and Clusters of Stars. Although the 4th Earl built a smaller 3 ft equatorial in 1876, the six-foot telescope remained in use until about 1890. After his death in 1908, the telescope was partly dismantled, and in 1914, one of the mirrors with its mirror box was transferred to the Science Museum in London. The walls remained. The tube, second mirror box, and universal joint survived. Reconstruction Following a TV programme, lecture, and book by Patrick Moore, there was renewed interest in the six-foot telescope in the 1970s. Gradually, the telescope became a visitor attraction. But it was not until the 1990s that plans to actually rebuild the telescope came to fruition. In 1994 the retired structural engineer and amateur astronomer Michael Tubridy was called in to research and re-design the Rosse six-foot telescope. The original plans were lost, and so it took detective work to review the remains of the telescope, incidental comments in observing logs, and contemporary photographs taken by Mary Rosse, wife of the 3rd Earl. Reconstruction work lasted from early 1996 to early 1997. It had been planned to include a working mirror, but due to budget constraints this had to be left for a separate project. The new mirror was installed in 1999. Unlike the speculum original, and unlike modern aluminium- or silver-coated glass mirrors, this is made of aluminium, as a compromise between authenticity and utility in astronomical observation. Modern companion radio telescope In 2017, LOFAR