Doppler shift of a hydrogen spectral line* One of the most prominent spectral lines of hydrogen is the Hα line, a bright red line with a wavelength of 656.1 × 10-9 m.
(a) What is the expected wavelength of the Hα line from a star receding with a speed of 3000 km/s?
(b) The Hα line measured on Earth from opposite ends of the Sun's equator differ in wavelength by 9×10-12 m. Assuming that the effect is caused by rotation of the Sun, find the period of rotation. The diameter of the Sun is 1.4 × 106 km.