SN 1006

SN 1006 was a supernova that was probably the brightest stellar event in recorded history. 
It got to about −7.5 visual magnitude, more than sixteen times the brightness of Venus. This "guest star" was described by observers across China, Japan, Iraq, Egypt, and the continent of Europe. Modern astronomers now think its distance from Earth was about 7,200 light-years.
It was likely a white dwarf star that had been pulling matter off an orbiting companion star. When the white dwarf mass exceeded the stability limit (known as the Chandrasekhar limit), it exploded.