Using the velocity of light how can i devise a strategy to find out when the Crab Nebula occurred ?

Question

In A.D 1054 the Chinese astronomers saw the explosion

Answer 1

A supernova takes place.  It shines a great light in all directions.  This might cause a light echo, if some of that light has reflected off of dust and gas in the galaxy.  We know the speed of light, if we can determine the angular size of a light echo, you'll be able to determine when it occurred and how far away it is.

Answer 2

I'm not sure what you are asking?

The supernova that caused the nebula was observed in 1054

So why do you need to work this out?

Answer 3

Well, if some current research and estimations are correct, the Crab Nebula (M1) is approximately 6,500 light years away.  So, if the Supernova that created it was seen from earth in 1054 A.D. that would mean the explosion occurred around 5,446 B.C.  

However, there are some uncertainties as to it's true distance, due to inconsistent data for all the currently known methods of measuring distance.  Some distance estimates are only 6,300 light years away.  And the expansion rate of the Crab Nebula can make this ever more confusing.

Answer 4

Say the Crab Nebula is about 1000 light years away.  If observers saw the explosion about 1054, then the actual explosion occured 1000 years before that, in AD54.

Now... if the actual distance to the Crab Nebula is 6487 light years away....