Although the universe witnesses a massive star exploding about once every second, such supernova blasts are spread throughout more than 100 billion galaxies. If you narrow the focus to just our home galaxy, the Milky Way, the number of these so-called core-collapse supernovae dwindles to roughly one each century. But the most recent one visible from Earth occurred in the 17th century. It gave birth to the Cassiopeia A supernova remnant.
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