William of Hirsau

William of Hirsau (or Wilhelm von Hirschau) (c. 1030 – 5 July 1091) was a Benedictine abbot and monastic reformer. He was abbot of Hirsau Abbey, for whom he created the Constitutiones Hirsaugienses, based on the uses of Cluny, and was the father of the Hirsau Reforms, which influenced many Benedictine monasteries in Germany. He supported the papacy in the Investiture Controversy. In the Roman Catholic Church, he is a Blessed, the second of three steps toward recognition as a saint.

William was born in Bavaria, possibly in about 1030; nothing more is known of his origins. As a puer oblatus entrusted to the Benedictines he received his spiritual education as a monk in St. Emmeram's Abbey, a private church of the Bishop of Regensburg, where the famous Otloh of St. Emmeram was William's teacher. It is generally believed that it was here that William first became friends with Ulrich of Zell (later distinguished as a Cluniac reformer and a saint), a friendship which lasted to the end of his life.

Also in the abbey, about the middle of the 11th century, William composed learned treatises on astronomy and music, disciplines that formed part of the quadrivium, in the knowledge of which William was considered unsurpassed in his day.

He constructed various astronomical instruments, made a sun-dial which showed the variations of the heavenly bodies, the solstices, equinoxes and other sidereal phenomena. His famous stone astrolabe can still be seen today in Regensburg: more than 2.5 metres high, it is engraved on the front with an astrolabe sphere, while on the reverse side is the figure of a man gazing into the heavens, presumed to be the Greek astronomer and poet Aratos of Soloi (of the 3rd century B.C.).

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