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History of the Telescopes

Click Here to View the Astronomy SlidesThe 72 inch telescope after restoration
© Birr Castle Archives
"Visitors to Birr have sometimes commented on the absence of any biography of my great-grandfather and grandfather, remarking that the lack is curious in view of their contributions to scientific knowledge. I believe that two main reasons have accounted for this till the present time. First, they never kept the results of their observations to themselves; all discoveries were reported immediately to the relevant scientific publications of the day, and therefore became common knowledge. Secondly, some of their major deductions were so revolutionary that, in default of any outstanding proof, they were not generally accepted by other scientists of the time. It is only in quite recent years that the general correctness of my great-grandfather's conclusions, reached by his studies of the galaxies, has been proved. Similarly, my grandfather's estimate of the heat of the moon is now known to have been absolutely right."

The opening words by Laurence Michael, Sixth Earl of Rosse from the forward of "The Astronomy of Birr Castle" by Patrick Moore", originally published in 1971.

During the 1840's and starting from virtually first principles, the third Earl of Rosse designed and had built the mirrors, tube and mountings for a 72 inch reflecting telescope which was the largest in the world at that time and remained so for three quarters of a century. With this instrument, situated near the middle of Ireland, Lord Rosse was able to study and record details of immensely distant stellar objects and to provide evidence that many of these mysterious nebulae were actually galaxies located far outside our own.

Click Here to View the Astronomy SlidesIllustration of the 72 inch Telescope
© Birr Castle Archives

The future third Earl of Rosse, William, was given the title of Lord Oxmantown from his birth on the 17th of June, 1800. He was the eldest of three sons, all of whom were educated at home in Birr by private tutors rather than being sent to public schools in England. This type of education may have greatly helped William's natural instinct for engineering, practical aspects of which surrounded him on the Birr Castle demesne. Private tuition gave way to a university education when William was 18 years old. He then went to Oxford College, and graduated with a first class honours Mathematics degree in 1822. William joined the Royal Astronomical Society in 1824 and represented Co. Offaly (at that time known as King's County) from 1823 to 1834 in the House of Lords, supporting both Catholic Emancipation and the Reform Bill. He retired from politics to pursue his scientific and engineering interests and in 1836 he married Mary Wilmer-Field, a wealthy heiress from Yorkshire. The financial security from this marriage, as well as the ownership of Birr Castle (which his parents granted him before they left Ireland to live in Brighton, England) allowed him to realize his scientific ambitions and plans. In 1828 he published his first experimental results regarding the grinding and publishing of telescope mirrors in the Edinburgh Journal of Science. At the outset of his career William decided to publish all his results, in marked contrast to many other telescope makers. In 1831, he joined the British Royal Society (and was its president from 1848 to 1854).

The first major telescope built by Lord Rosse was based around a 36 inch (91 cm) mirror. After experimenting with copper and tin alloys for the metal reflecting surface and developing his own steam-driven mirror grinding machine, this telescope was completed in 1839. It was supported in a frame which was a modification (and improvement) of a design by William Herschel. A circular track allowed this telescope to reach most areas of the sky. Despite this telescope being "home-built" (the mirror was cast in the grounds of Birr Castle) two contemporary expert observers confirmed it's quality and performance, which allowed significantly increased resolution of stellar objects, one of them (Dr. Thomas Robinson of the Armagh Observatory) calling it the most powerful instrument of it's time. Lord Rosse used the 36 inch telescope to study the Moon in greater detail than was previously possible, under a magnification of 900 times. He also studied star clusters and nebulae (fuzzy patches of gas) which earlier telescope were incapable of resolving to any great degree.

Click Here to View the Astronomy SlidesLady Rosse, The Fourth Earl and Dr. Boeddicker
© Birr Castle Archives

Lord Rosse spent over three years building his next large telescope, "The Leviathan of Parsonstown" based around a 72 inch (183 cm) mirror, with which he hoped to confirm that some of the nebulae contain stars, hints of this being given by the 36 inch telescope. This telescope was basically a 17 m tube, suspended between two 15 m high walls, with a network of supports which enabled the tube to be moved freely in a vertical direction, but restricted horizontal movement to the extent that the total viewing time on any particular object varied from about 50 minutes for an object at the equator to about 2 hours for an object at the highest level. The vertical movement was contained between the lowest level of 15 degrees elevation and the highest level of 15 degrees beyond the vertical, i.e. a total vertical travel of 90 degrees. Again the mirror was cast in the grounds of the Castle, using 3 large crucibles and resulting in a mirror that weighed over 3 tons. Construction of the telescope and mountings took over 2 years but finally, on 15 February 1845, the weather cleared long enough for a short viewing of the double star Castor, which confirmed the potential of the new telescope. In April 1845, Lord Rosse was able to deduce the spiral nature of the M51 nebulae.

Click Here to View the Astronomy SlidesA drawing of the 72 inch telescope in its viewing position
© Birr Castle Archives

The potato famine in Ireland prevented regular use of the telescope until 1848. The telescope was initially used to view Jupiter and the moon, although the bulk of the work done by the 72 inch was in the area of nebulae and star clusters. At the time it was commonly thought that these gas clouds were part of our galaxy. Lord Rosse observed many nebulae and was able to resolve spiral arms, indicating that at least some of the nebulae were more than just collections of gas. In 1923 Edwin Hubble showed, through his measurement of the distance of variable stars, that some of the starry nebulae were in fact galaxies separate (and in many cases larger), than our own.

Click Here to View the Astronomy SlidesM51, a spiral galaxy 37 million light-years distant
© Birr Castle Archives

Lord Rosse also realised that he was observing edge-on spiral objects and by the end of 1850, the number of spiral objects seen had reached fourteen. He made drawings of the objects he observed (astronomical photography was well established by the time of the fourth Earl, but the 72 inch telescope was too unsteady for the long exposures required), and noted various types of spirals. Lord Rosse studied M1 (The first object in Charles Messier's list of over 100 star clusters and nebulae) naming it the Crab Nebula, along with many other nebulae, including M51, M87 and the planetary nebula M27. Use of the telescope was hampered however, by the cloudy Irish weather and the necessity of replacing the metal mirror which tarnished quickly, with the backup mirror, at regular intervals.

In addition to Lord Rosse, visiting astronomers from many parts of the world came to use the telescope and it's fame was such that it is referred to in Jules Verne's early Science Fiction novel "From the Earth to the Moon"

"The distance which had then separated the projectile from the satellite was estimated at about two hundred leagues. Under these conditions, as regards the visibility of the details of the disc, the travelers were farther from the moon than are the inhabitants of earth with their powerful telescopes. Indeed, we know that the instrument mounted by Lord Rosse at Parsonstown, which magnifies 6,500 times, brings the moon to within an apparent distance of sixteen leagues."

Among the astronomers who took advantage of the telescopes unequalled light gathering power were J.L.E Dreyer, who later compiled the New General Catalogue of clusters and nebulae. Lord Rosse's son Laurence who became the fourth Earl on the death of his father in 1867 also used the telescope regularly and made the first accurate estimate of the temperature of the Moon. However, the instrument used for this work was the 36 inch reflector, which the fourth Earl had fitted with a drive to enable tracking of the Moon's movement. The 72 inch telescope was used less frequently and on the death of the fourth Earl it was dismantled.

The third Earl of Rosse occupies an important position in the history of astronomy. In the words of Professor Sir Bernard Lovell:

"He succeeded in an almost impossible task, the measure of which can be appreciated from the fact that his telescope remained the largest in the world for three-quarters of a century......The Birr Telescope is a tribute to the third Earl's skill in engineering and optics: the results he obtained with it are a remarkable tribute to his observational skill and to his insight that such a device would record more of the depths of the universe than man had yet conceived. I have before me two illustrations of the nebula in Canes Venatici- a galaxy more than ten million light years away in space. One is a drawing made by Lord Rosse as he saw it in the Birr telescope. The other, a photograph taken a century later by the 200 inch telescope on Mount Palomar. The identity of the two is dramatic and the spiral form of the galaxy is shown with far greater form in the drawing. It is to the everlasting credit of Lord Rosse that he discovered the spiral structure of the nebulae and thereby opened an avenue of exploration which today has lead us into the inconceivable depths of space and time."

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