A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that the stars .

Have different temperatures

Explanation:

A star spectra shows how bright it appears from the earth. It is composed mainly of thermal radiation that produces a continuous spectrum. However there exist a relationship between the temperature of the start and its spectrum.

As the temperature of the star increases, the peak of its continuous spectrum shift to shorter (bluer) wavelengths. A blue or white start is hotter than a yellow start which is in turn hotter than a red star. These variations in temperatures in the main reason why all stars don't look alike.