A distant galaxy isobserved to have its hydrogen-b line shifted to a wavelength of 580 nm, away from its laboratory wavelength of 434 nm. Which of the following gives the approximate velocity of recession of the distant galaxy? (Note: $$\frac{580}{434}=\frac{4}{3}$$)

How could the recession speed be 0.28c?

## GRE0877 Q#55

### Re: GRE0877 Q#55

You have to apply the relativistic doppler effect (http://en.wikipedia.org/wiki/Relativist ... ler_effect)

$$\frac{\lambda_o}{\lambda_s} = \sqrt{\frac{1+\beta}{1-\beta}}$$

The fraction on the left is 4/3, as the question said. So you just have to solve for beta, and beta=0.28 works. (beta=v/c)

$$\frac{\lambda_o}{\lambda_s} = \sqrt{\frac{1+\beta}{1-\beta}}$$

The fraction on the left is 4/3, as the question said. So you just have to solve for beta, and beta=0.28 works. (beta=v/c)

### Re: GRE0877 Q#55

Thank you... with 9677 and 0877 for practice materials I will continue studying for the April test.TakeruK wrote:You have to apply the relativistic doppler effect (http://en.wikipedia.org/wiki/Relativist ... ler_effect)

$$\frac{\lambda_o}{\lambda_s} = \sqrt{\frac{1+\beta}{1-\beta}}$$

The fraction on the left is 4/3, as the question said. So you just have to solve for beta, and beta=0.28 works. (beta=v/c)