One way astronomers detect planets orbiting around a distant star is by using the Doppler shift of light from the star. When a planet orbits a star, the star also moves in a circular orbit centered on a point that lies between the star and the planet. (See Chapter 5.) Light from the distant planet will also be Doppler shifted due to the planet’s motion. To study this phenomenon, let’s consider the simpler case of light from the planet. Assume a planet like the Earth that orbits a star like our Sun and consider visible light with f_source = 6.0 x 10¹⁴ Hz (l  500 nm) emitted by the planet. What is the Doppler shift of this radiation when the planet is moving directly toward the Earth? Assume the speed of the planet relative to the Earth is the same as the speed of the Earth as it orbits the Sun. Express your answer in the form (f_obs=  f_source)/f_source and assume the planet is moving toward the Earth. Note: Light from such a distant planet is not usually detected since it is much weaker than light from the star. Instead, astronomers measure the Doppler shift of the star’s light, which is smaller than that found here since the star’s orbital velocity is much less than the planet’s velocity.