The Comet is a name given to an artificial comet within the Sol System. Built from unknown origins during the Dark Age of Technology, the structure orbits the Sol System and appears over Terra every thousand years. During one such appearance over Terra, the Unification Wars were coming to an end and the Emperor decided to intercept The Comet and modify it as a shrine for his victory.
Subsequently during the Great Crusade, the Word Bearers built a shrine to worship the Emperor on the structure. After the Word Bearers were reprimanded at Monarchia, Sor Talgron was secretly charged by Lorgar to dismantle the shrine, though in truth this was just a cover story to conceal his sabotage of the Imperial Palace.