Chapter 6, Problem 1AA

An astronomer measures the speed of recession of a remote galaxy to be 365 km/s using the Doppler principle According to the Hubble relation, about how far away is the galaxy?

To determine

The distance of a remote galaxy if speed of recession is $\text{365}\text{km}/\text{s}\text{.}$

Answer to Problem 1AA

The distance of the distant galaxy is $17.38\text{mly}\text{.}$

Explanation of Solution

Given info:

  $\begin{array}{l}v=365\text{km/s}\\ \text{where}\\ v=\text{velocity of recession}\end{array}$

Formula used:

Hubble’s relation

  $\begin{array}{l}v=H_{o}D\\ H_o=\text{Hubble}’\text{s constant},\left(\text{21km}/\text{s}/\text{mly}\right)\\ D=\text{Distance}\end{array}$

Calculation:

Substitute the given values

  $\begin{array}{l}v=H_{o}D\\ 365\text{km/s}=(21\text{km/s/mly})\times (D)\\ D=\frac{365}{21}=17.38\text{mly}\end{array}$

Conclusion:

Thus, the distance of the distant galaxy is $17.38\text{mly}$ .