An astronomer observes a hydrogen line in the spectrum of a star. the wavelength of hydrogen in the laboratory is 6.563 x 10-7m, but the wavelength in the star's light is measured at 6.56186 x 10-7m. which of the following explains this discrepancy? a. the star is moving away from earth b. the wavelength of light that the star is emitting changes constantly. c. the frequency of light that the star is emitting changes constantly. d. the star is approaching earth.