Chapter 33, Problem 8Q

To determine

How the Cepheid variable star is used to measure the distance to galaxies?

Answer to Problem 8Q

Solution:

$Distance\left(inparsecs\right)=10parsecs\times \sqrt{\frac{\text{luminosity}}{\text{observed}\text{brightness}}}$

Explanation of Solution

Step 1: Observe the brightness of the star to find out the time period

Step 2: Use the luminosity-time period graph to find the corresponding luminosity

Step 3: Use the luminosity and the average observed brightness to calculate the approximate distance using the formula:

$Distance\left(inparsecs\right)=10parsecs\times \sqrt{\frac{\text{luminosity}}{\text{observed}\text{brightness}}}$