Can someone please help me anwser this astronomy question?

Question

The Crab Nebula is now about 1 parsecs in radius. If it was observed to explode in A.D. 1054, roughly how fast is it expanding? (Assume a constant expansion rate. Is that a reasonable assumption?)

Answer 1

Just take the difference between today and AD 1054 for your time. Then divide the distance (1parsec) by that time to get the speed.

It's that easy.

Answer 2

Constant expansion rate is a reasonable assumption.  The speed is so high relative to the mass, that it will never re-collapse due to gravity ... and barely even slows down.

1parsec/(2008-1054) = 1parsec/954year

1 parsec = 3.1x10^16 m = 3.1x10^13km

1year = 365day*24hr/day = 8760hr

(3.1x10^13km)/(954*8760hr) = 3.7x10^6 km/hr

Answer 3

speed = distance / time