supernova light can echo through time

http://www.symmetrymagazine.org/article/august-2015/all-about-supernovae

"Just as your voice echoes when its sound waves bounce off a surface and come back again, a supernova echoes in space when its light waves bounce off cosmic dust clouds and redirect themselves toward Earth.

Because the echoed light takes a longer, more scenic route to our planet, this phenomenon offers a portal to the past, allowing scientists to look at and decode supernovae that occurred hundreds of years ago. One example of this is SN1572, or Tycho’s supernova, a thermonuclear supernova that occurred in 1572. This supernova shined brighter than Venus, was visible in daylight and took two years to dim from the sky.

More than four centuries later, in 2008, original light from this historical supernova became visible to astronomers once again. Because the light originated from the cosmic demolition site of the original star, scientists knew that it must have come from Tycho’s supernovae. Although the light was 20 billion times fainter than what Tycho Brahe observed in 1572, scientists were able to analyze its spectrum and classify the supernovae as a greedy white dwarf, or a thermonuclear supernova."