Events

• February—Battle of Mortemer: The Normans defeat a French army as it is caught pillaging and plundering. King Henry I of France withdraws his main army from Normandy as a result.

• April 30, Rosdalla Ireland: Earliest known European tornado.

• July 4—The SN 1054 supernova is recorded by the Chinese, Arab and possibly Native Americans near the star ζ Tauri. For 23 days it remains bright enough to be seen in daylight. Its remnants form the Crab Nebula (NGC 1952).

• July 16 – Cardinal Humbertus, a representative of Pope Leo IX, and Michael Cerularius, Patriarch of Constantinople, decree each other's excommunication. Most historians look to this act as the final step in the initiation of the Great Schism between the Roman Catholic and Orthodox Christian Churches. In 1965, those excommunications are rescinded by Pope Paul VI and Patriarch Athenagoras when they meet in the Second Vatican Council. However, to this day each church claims to be the One Holy Catholic and Apostolic Church and each denies the other's right to that name. (See East-West Schism)

• July 27 – Siward, Earl of Northumbria invades Scotland to support Malcolm Canmore against Macbeth, who usurped the Scottish throne from Malcolm's father, King Duncan. Macbeth is defeated at Dunsinane.

Deaths

• April 19—Pope Leo IX (b. 1002)

• September 24—Hermannus Contractus

• Yaroslav the Wise, prince of Kievan Rus