What speed should a galaxy move with respect to us so that the sodium line at `589.0 nm` is observed at `589.6 nm` ?

Explanation

`(Delta lambda)/(lambda) = (V)/(C),`
`V = +c ((0.6)/(589.0)) = 3 xx 10^(8)((0.6)/(589.0))`
` = + 3.06 xx 10^(5) ms^(-1)`
Therefore, the galaxy is moving away from us with speed 306 km/s