Observations of the crab nebula taken over several decades show that gas blobs that are now 100 arcseconds from the center of the nebula are moving away from the center by about 0.11 arcsecond per year. use that information to estimate the year in which the explosion ought to have been observed.

Estimation: year 1110.

Explanation:

We need to know how much time it takes to move 100 arcseconds if it moves at 0.11 arcsecond per year. Similarly to any velocity equation , where in our case the distances are angular, we will obtain the time by doing:

Which, considering from 2019, the explosion ought to have been observed around 1110 (in reality it was observed by Chinese astronomers in 1054).