Since 6 kiloparsecs is ca. 20,000 light-years the cosmic event itself happened ca. 18,000 BC.
The supernova was first observed on October 9, 1604. The German astronomer Johannes Kepler first saw it on October 17, but he studied it so extensively that the supernova was subsequently named after him. His book on the subject was entitled De Stella nova in pede Serpentarii (On the new star in Ophiuchus's foot).
It was the second supernova to be observed in a generation (after that seen by Tycho Brahe in Cassiopeia in 1572). No further supernovae have since been observed with certainty in the Milky Way, though others outside our galaxy have been seen.