How can stars be distinguished from quasars by observation?

In the photographs, the quasars look like star-shaped objects, so they cannot be recognized by their appearance. The differences between them are manifested in the spectra. In contrast to stars, the spectra of quasars contain bright and broad emission lines. In this case, the spectral lines are strongly redshifted due to the Doppler effect (as in distant galaxies). In addition, quasars are sources of radio emission.

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