It is one of the brightest sources of high-energy radiation in the sky. Little wonder, it's the expanding remains of an exploded star, a supernova seen in the year 1054. SN 1054 is a supernova that was first observed on 4 July 1054, and remained visible for around two years. The event was recorded in contemporary Chinese astronomy and references to it are also found in a later (13th-century) Japanese document, and in a document from the Arab world. The remnant of SN 1054, which consists of debris ejected during the explosion, is known as the Crab Nebula.