The only information that we have is from the light that is imaged by our telescopes. Fortunately, light contains a wealth of physical information about the Universe. The frequency is the number of wave crests that pass by a detector per second of time. This speed is constant throughout space for all wavelengths. In the visible, the rainbow of colors make up the spectrum.
Color is the same as wavelength .
Blue light has the shortest wavelength and red light has the longest. The atmosphere is mostly opaque to the electromagnetic spectrum. The Doppler Effect is the shift of the wavelength of light produced by motion of an object toward or away from us. The change in the wavelength between that observed for a moving object and that measured when the light source is at rest is directly proportional to the wavelength. For stars moving away from us, the wavelength change is toward the red and is called a redshift .