On September 2, 1918 Ellison was appointed Director of the Armagh Observatory.

He returned to Ireland in 1937 to become director of the Armagh Observatory.

In 1882 he relocated again, this time to Armagh Observatory, where he served as Director until his retirement in 1916.

Such a model, called a human orrery, has been laid out with precision at the Armagh Observatory.

Hardcastle was supposed to become the director of Armagh Observatory, however he died before he could take up his post.

It is named for the Armagh Observatory.

He designed the principal buildings of the Armagh Observatory which began construction in 1789.

In 1790 he founded the Armagh Observatory as part of his plan for a university in Armagh.

The educational tradition continued with the foundation of the Royal School in 1608 and the Armagh Observatory in 1790.

Later he was active at the Armagh Observatory in Northern Ireland.