Hello I have a question that is giving me trouble: Light of wavelength 659.7 nm is emitted by a star. The wavelength of this light as measured on Earth is 661.1 nm. How fast is the star moving with respect to Earth? km/s Is it moving toward Earth or away from it? Here's where I'm at. I have reasoned that since the wavelength is increasing that the star is moving away. My main problem is determining the frequency of the light. I assume that I can use the formula: velocity = wavelength * frequency however the frequency I get just seems wrong. The units are throwing me off too, any help would be greatly appreciated.