one of the few supernovae (violent stellar explosions) known to have occurred in the Milky Way Galaxy. Jan Brunowski, Johannes Kepler's assistant, first observed the phenomenon in October 1604; Kepler studied it until early 1606, when the supernova was no longer visible to the unaided eye. At its greatest apparent magnitude (about -2.5), the exploding star was brighter than Jupiter. No stellar remnant is known to exist, though traces of nebulosity are observable at the position of the supernova. Like Tycho's Nova, Kepler's served at the time as evidence of the mutability of the stars.