Second note ... From the Internet.
Red Shift & Blue Shift A light source moving away from the listener (v is positive) would provide an fL that is less than fS. In the visible light spectrum, this causes a shift toward the red end of the light spectrum, so it is called a red shift. When the light source is moving toward the listener (v is negative), then fL is greater than fS. In the visible light spectrum, this causes a shift toward the high-frequency end of the light spectrum.
Adding to that, two objects parting at more than the speed of light would not be visible to each other.
Very true. However, in math, things can be calculated that are not possible in physics. For example, 186,200 miles per second times 2 equals 372.4 miles per second ;0)