The distance to SN 1987A is about 170,000 ly. How long ago did the supernova occur? If the burst of.

The distance to SN 1987A is about 170,000 ly. How long ago did the supernova occur? If the burst of neutrinos arrived at Earth 4 hours before the first light from the explosion arrived (22 hours before humans noticed it), did the neutrinos leave just before, or just after, or at the same time, as the light? (Hint: Reread Section 1-2, and review information about neutrinos in Section 8-3.) (Notes: The speed of light is 3.0 3 105 km/s; 1 ly _ 9.5 3 1012 km.)