I've been meaning to write this up for a few weeks now because I think the idea is so amazing. A few weeks ago Universe Today wrote Astronomers 'Time Travel' to 16th Century Supernova.
"On November 11, 1572 Danish astronomer Tycho Brahe and other skywatchers observed what they thought was a new star. A bright object appeared in the constellation Cassiopeia, outshining even Venus, and it stayed there for several months until it faded from view. What Brahe actually saw was a supernova, a rare event where the violent death of a star sends out an extremely bright outburst of light and energy. The remains of this event can still be seen today as Tycho’s supernova remnant. Recently, a group of astronomers used the Subaru Telescope to attempt a type of time travel by observing the same light that Brahe saw back in the 16th century. They looked at 'light echoes' from the event in an effort to learn more about the ancient supernova."
See the article for more info, but I'm still baffled how they did it. Simplistically sure, some of the light from the supernova came straight to earth, that's what people saw in 1572. Light moving in a different direction could have reflected off a dust cloud back at earth and since it took a longer path, would take longer to get here. How astronomers figured out where it would reflect off, and when it would arrive here I have no idea. That's pretty astounding work.
The Nature paper is here, though I don't have access to more than the abstract.
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