Village of Birr

In 1845 William Parsons, the third Earl of Rosse, constructed the largest telescope in the world on his estate in the heart of Ireland. The mirror was six feet in diameter, nearly twice the size of any previously attempted. At that time the village surrounding Lord Rosse's castle was known as Parsonstown and the astronomical world referred to the giant telescope as "The Leviathan of Parsonstown". Although Ireland is generally a poor location for a large telescope due to the often cloudy skies, this telescope made one outstanding discovery, namely that the nebula M51 (the fifty first object on Charles Messier's list) had a spiral structure. Subsequently, a number of other spiral nebulae were discovered at Birr and elsewhere. At the time of discovery, many thought that M51 and the other spirals were solar systems in formation. Today, however, we know that they are distant galaxies comprised of billions of stars and that our home galaxy, the Milky Way, is itself a spiral.

I presented a talk on this telescope at the December 2001 meeting of the Orange County Astronomer's. You can listen to it by clicking here: OCA Talk

After Irish independence, Parsonstown was renamed Birr to reflect its Irish roots. Today Birr is a quite agreeable place with shops, pubs, and interesting architecture, many dating from the Georgian period (late eighteenth century).

Birr castle is still occupied by the Parsons family; the current proprietor is the seventh Earl of Rosse. The castle played a role in much of Ireland's turbulent history, and was besieged by cannon in 1643. The third Earl who built the telescope and his son were interested in all aspects of science, and Birr became a center of scientific activity towards the end of the nineteenth century. There is a science museum on the castle grounds which has a number of interesting displays and artifacts from this period.

The telescope fell into disuse around 1908 and was a graceful ruin for most of the 20th century. In 1997 the telescope was refurbished with funding from the Republic of Ireland and the European Union. It is now fully operational, with a new optical system and reinforced mounting.


Rear view of telescope	Close-up of eyepiece assembly	Lord Rosse's most famous discovery

The first photograph above shows the pulley system and crank used to move the telescope. Due to the fact that the supporting walls are fixed, an object can be tracked for no more than forty five minutes or so. However, this insures that the object is always observed near the meridian, the position giving the steadiest image.

The second photograph shows the eyepiece assembly. Incredibly, the instrument was never fitted with a finder. Objects were located using a wide field eyepiece (covering about 1/2 degree of sky) then, a shorter focal length lens was slid into place for detailed observation.

Finally, a coffee shop acknowledges Birr's most important claim to fame: M51, the Whirlpool Galaxy.


72" Telescope	72" Mirror in Science Center	Telescope and Castle


St. Brendan's Church	Connaught Street	Castle Street


Castle	Gardens	Ivy "Cloister"