The Observatory, like several of the Archbishop’s foundations, was built on a hill so that it could be seen against a natural woodland setting from his new palace. It was designed by Francis Johnston, the city architect, who was responsible for several fine buildings in Dublin; notably, the Chapel Royal and the GPO in O’Connell Street. The new observatory was the second to be established in Ireland; (the first was Dunsink Observatory near Dublin). It is the oldest scientific institution in Northern Ireland.
In some 17th C observatories, notably Paris (1667), the architectural elegance of the structure was considered more important than its practicality for astronomy This was true to a lesser extent in Wren’s design for the Royal Observatory (1675) at Greenwich where, in spite of its grand facade, the structure did not actually impede observations. Normally, at that time, observations were made from either an outside platform or alternatively from inside a large room with tall windows. The instruments were usually portable, with a mounting which simply rested upon a table or the floor and therefore were easily shaken by the movement of people across the room. As instruments increased in size during the 18th and 19th centuries they required more substantial support to avoid vibration.
The buildings of Dunsink (1785) and Armagh (1790) Observatories represent a revolution in observatory design. At Dunsink and Armagh, for the first time, the requirements for the stability of the instruments took priority over aesthetic considerations. Unlike the dome of the King’s Observatory, Kew (1768), which is insubstantial and appears almost as an afterthought, the domes at Dunsink and Armagh dominate the structure and form the central theme of the building. In addition the stability of the instruments was guaranteed by placing them on substantial stone pillars brought up from the substrata below the building. At Dunsink these pillars were free standing and not joined to the rest of the building. In this way, any vibrations originating in the main part of the structure, were not transmitted to the instruments. These principles of construction have been employed in most subsequent observatory buildings throughout the world.