What makes a star's spectrum appear to be different from another star's?

If a star is moving toward Earth, its light waves seem to be squeezed together. The decreasing distance between Earth and the star shortens the wavelength of the starlight received by Earth. This shifts the star's spectral lines toward the blue end of the spectrum. If the star is moving away from us, its waves are effectively stretched out when they reach Earth, increasing their wavelength. This shifts the star's spectral lines toward the red end of spectrum. Dark lines in stellar spectra are being caused by absorption of wavelengths of energy by the elements in the star's outer levels. patterns of absorption lines that appear at shorter or longer wavelengths than normal indicate that the star is moving. The greater the shift from the normal position of the lines, the faster the star is moving.