Four hundred years ago this week, a previously unseen star suddenly appeared in the night sky. Discovered on Oct. 9, 1604, it was brighter than all other stars.
The German astronomer Johannes Kepler studied the star for a year, and wrote a book about it titled "De Stella Nova" ("The New Star"). In the 1940s scientists realized the object was an exploded star, and they called it Kepler's supernova.
No supernova in our galaxy has been discovered since the 1604 event.