by KEN CROSSWELL
A newly measured distance to stellar debris in the northern sky links it more firmly to an explosion observers saw in 1181
Every year astronomers see hundreds of supernovae erupt in other galaxies, but from such great distances these stellar explosions look only like bright dots. Researchers therefore prize the few supernovae that past observers witnessed in the Milky Way, where telescopes can scrutinize the wreckage. Since the year A.D. 1000, skywatchers have seen five of our galaxy’s stars die in brilliant explosions. Now a new distance determination to the most mysterious of these is yielding new insight into its nature.
All five stars blew up thousands of light-years away, so their light took many millennia to reach us. But observers can recognize celestial events only when their light strikes Earth, and astronomers therefore usually say they occur that same year. Four of the five post-1000 supernovae are famous: A 1006 explosion in the southern sky was the brightest in recorded history; a 1054 supernova in the constellation Taurus spawned the well-known Crab Nebula; and supernovae in 1572 and 1604 bear the names of two Renaissance astronomers, Tycho (Brahe) and (Johannes) Kepler.
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