Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?
A) you must find a Cepheid variable star in the galaxy
B) you must take a spectrum of the galaxy and measure the red shift
C) you must measure how strongly the galaxy emits radio waves at a wavelength of 21 centimeters
D) you must find a Type Ia supernova that is exploding in that galaxy
E) all you need to do is look at the galaxy through any telescope

Question

Quizplus · Accepted Answer

To use Hubble's Law to get the distance to a galaxy, we must measure the redshift of the galaxy, which can be done by taking a spectrum of the galaxy. The redshift is then used to calculate the galaxy's recessional velocity, which can be used with Hubble's Law to calculate the distance to the galaxy. The other options listed can be used for other distance measurement methods, but not for the use of Hubble's Law.

Before You Can Use Hubble's Law to Get the Distance