1. The problem statement, all variables and given/known data When studying the optical spectrum of a very distant quasar (quasi stellar object), they found that a certain spectral line appears at a wavelength of 559 nm instead of the regular 446 nm. In terms of the speed of the light, what is the radial speed of the quasar with respect to Earth? 2. Relevant equations 3. The attempt at a solution I tried using the fact that the redshift z= (λ_observed - λ_emitted)/(λ_emitted) and then 1 + z = 1/(sqrt(1-(v^2/c^2)) and then solving for v.. But is this "v" the orbital velocity? And I did convert my answer into terms of the speed of light so that's not the part that's wrong. Any help? Thanks!