Astronomers and their tools - Lord Rosse's 72-inch Telescope

Birr Castle
Birr Castle. Lord Rosse was able to finance the Leviathan by marrying a wealthy Yorkshire heiress.
Birr Castle
Birr Castle, Demesne. Lord Rosse's 72" telescope, the Leviathan of Parsonstown.
Leviathan
Leviathan. Note winding gear, bottom right.
Leviathan
Leviathan reaches the upper observing gallery. Note graduated azimuth beam.
Telescope
The lower gallery carrying the observing trolley halfway up the track on the inclined ladders. For demonstration purposes only, the telescope and observing platforms are now computer controlled.
Tracks for the trolley carrying the mirror can be seen leading to the mirror box.
Tracks for the trolley carrying the mirror can be seen leading to the mirror box.
Cantilevered upper observing gallery.
Cantilevered upper observing gallery.

The construction of Lord Rosse's 72 inch (183 cm) telescope took place over two year period (1844 to 1845). The telescope uses a 3 ton mirror and is suspended between two 14 m high stone walls. Originally, the telescope offered fantastic views of Jupiter and the moon but was later used to observe nebulae. In fact it was this telescope that helped Lord Rosse decipher spiral structure in the nebulae and led to his conclusion that some of the nebulae were more than just gas clouds. It was then over 80 years later that Edwin Hubble identified the nebulae as island universes or galaxies.

Great flank wall and meridian arc along one end of which the azimuth beam travels
Great flank wall and meridian arc along one end of which the azimuth beam travels. Note counterweight.

One of the more fascinating things about the telescope is that it was only free to move vertically as a result could not permit extended view of any particular object. Remeber back to Module 1 and the discussion about the movement of the stars in the night sky. Essentially, the observer would have to plan ahead deciding on which objects he wanted to observe and then wait for the objects to come within the range of motion of the telescope. The observations could then last only as long as the object remained within that range of motion. Depending on the actual hight of the object above the horizon, observing times varied from 50 min for objects just above the horizon to just over 2 hours for objects nearly at the zenith.

Birr Castel and Lord Rosse's Leviathan are located in the town of Birr, north of Dublin Ireland.