What speed should be galaxy move with respect to us to the sodium line at 589.0 nm is observed at 589.6nm?

Explanation

Since `v lamda=c, (Delta v)/v=-(Delta lamda)/(lamda) `(for small changes is v and `lamda`) for `Delta lamda=589.6-589.0=0.6nm`
`:.(Deltav)/v=-(Delta lamda)/(lamda)=(v_("radial))/c`
or `v_("radial")~=+c(0.6/58.0)=+3.06xx10^(5)ms^(-1)=306km//s`
Therefore, the galaxy is moving away from us.