Telescope Discoveries

"The love of truth; the pleasure the mind feels in overcoming difficulties; the satisfaction of contributing to the general store of knowledge; the engrossing nature of a pursuit so exalted as that of diving into the wonders of creation; all these are very powerful incentives to exertion..."

Part of the Presidential address given by the third Earl to the 1854 meeting of the British Association for the Advancement of Science (giving some insight into his motives for the construction of his telescopes and also into the character of the man).

Lord Rosse spent a large part of his observing time on the 36 inch telescope studying the mysterious nebulae, such as M27 and the Great Nebulae in Andromeda. In these and other similar studies, the 36 inch telescope gave him tantalizing glimpses of possible clumps of stars within an otherwise fuzzy mass of gas. It was to improve the resolution of such nebulae that he built the 72 inch telescope.

The 36 inch also gave Lord Rosse views of the moon at magnifications up to 900, allowing exploration of aspects of the lunar topography never before observed. Dr. Thomas Romney Robinson wrote in 1840:

"It is scarcely possible to preserve the necessary sobriety of language, in speaking of the Moon's appearance with this instrument, which discovers a multitude of new objects at every point of its surface"

The smaller telescope was used by the fourth Earl to study spectra of eleven nebulae and observations using it showed that only 4 of them were gaseous, the rest exhibiting the continuous spectra characteristic of stellar objects. However, the installation of the spectrometer was not ideal and made for difficult observations.

Among the final work completed using the 36 inch telescope was measurement of the heat of the moon. Lord Rosse used the telescope to focus infrared radiation from the moon on a thermocouple to discover, in his own words:

"The greater part of heat received from the Moon consists of solar heat that has been first absorbed by the lunar crust, and then given off in dark radiation. No evidence of cosmical heat was obtained"

The first objects to be observed with the 72 inch telescope were the star Castor, which is one of the main stars in the constellation Gemini, followed by the star-cluster M67 in the Crab Nebulae. During the few occasions Lord Rosse used the telescope during the Irish Potato Famine he noted that M51 was a spiral nebula. 'Messier' described this object in 1774 as "a very small nebula without stars" but with his new telescope Lord Rosse was able to write in 1850:

"We thus observe, that with each successive increase of optical power, the structure has become more complicated. That such a system should exist, without internal movement, seems to be in the highest degree improbable.......The nebula itself however, is pretty well studded with stars"

By the end of 1850 Lord Rosse had resolved 14 nebulae into their spiral forms. Over the next two decades an intensive study of all the nebulae visible from Birr was undertaken. Among the nebulae on which records were kept were M77 (The Blue Spiral), M95 in the constellation Leo, the Triangulum Spiral (M33) and numerous others.

Robinson used the giant telescope to observe Jupiter and wrote on the 20th February 1848 that the dark brown belts on the planets presented:

"A remarkable appearance; they were full of faint striae running nearly parallel to them, and seemingly belonging to the brighter zones on each side"

Like the smaller 36 inch, the 72 inch telescope was used to observe the moon and in 1852 members of the British Association (Lunar Section) used it to investigate the possibility of creating a new map of the moon under various different lighting conditions.

Top

©The Birr Scientific and Heritage Foundation
Ireland's Historic Science Centre   Birr Co Offaly Ireland