Expert: Robi Bhattacharjee - 4/16/2009

Question
in AD 1054 chinese astronomers observed the light from a supernova in the night sky. This supernova was the incredidbly powerful origin of what is now the Crab Nebula.
  
  Using the valocity of light, devise and execute a strategy for finding out when the supernova actually occurred, relative to when the chinese astronomers saw the explosion.

 ''distance from earth to crab nebula  6500 light years''




1. what are some possible strategies for solving this problem?


2.of the strategies that u listed in (1) discuss the advantages and disadvantages of each?

Answer
Hi Ashley,

Well, light travels at one light year per year hence the name light year. So, in order for us to see the supernova, we would have to see the light it emits (after all, that's what seeing is). So since light takes a year to travel a light-year, it would take 6500 years to travel 6500 light years. So the actual supernova took place 6500 years before the Chinese astronomers saw it in 1054. So that means it took place in
5446 BC.

This strategy is foolproof since its logic is sound and there are no measurements needed. The only way this could go wrong is if the information provided, namely the distance from earth to the crab nebula and the year the astronomers saw it, was faulty.


I hope this helps,
Robi