You measure the redshift of a distant galaxy and find, using Hubble's law and assuming a Hubble constant of 70 km/s/Mpc, that its distance is 1 billion ly (310 Mpc).Imagine that an observer in that galaxy is measuring the recession speed of the Milky Way at the same time as your measurement.What would be the speed that the remote alien observer would record?
A) 700 km/s
B) 21,500 km/s
C) 3,400 km/s
D) 10,700 km/s
E) 6,300 km/s

Question

Quizplus · Accepted Answer

The correct answer is B.The recession speed of the Milky Way as measured by the remote alien observer would be 21,500 km/s. This is because the Hubble constant is the same for all observers, regardless of their location in the universe. Therefore, the recession speed of the Milky Way as measured by the remote alien observer would be equal to the Hubble constant multiplied by the distance to the Milky Way, which is 310 Mpc. This gives a recession speed of 21,500 km/s.

You Measure the Redshift of a Distant Galaxy and Find