SN-1987A was a supernova which occurred in the Large Magellanic Cloud, and was detected on Earth in 1987. When a supernova occurs, 100 times as much energy is emitted in neutrinos as in photons. SN-1987A was the first (and so far only) supernova to have occurred nearby to Earth after we built neutrino detectors capable of seeing the supernova neutrino burst. For SN-1987A, 24 neutrino events were detected by a number of detectors all over the Earth. 

1. The neutrinos from SN-1987A had an energy of approximately 20 MeV.  The rest mass of a neutrino is as yet unknown, but must be less than 1 eV/c2. 
2. Let us assume that the mass of a neutrino is 1 eV/c2. How much slower than light (in m/s) were the neutrinos from SN-1987A moving? If the neutrinos were lighter, how would this answer change?
3. SN-1987A occurred at a distance of 51.474 kpc from Earth. Assuming a neutrino mass of 1 eV/c2, what was the elapsed time between the emission of a neutrino from SN-1987A and our detection of it here on Earth, according to the neutrino?