Final answer:
The red or blue shifts observed in spectral lines by astronomers are due to the Doppler effect. By measuring the wavelengths of the absorption lines in the spectrum of an object, astronomers can detect the Doppler shift and determine the radial velocities of distant objects, such as stars and quasars.
Step-by-step explanation:
The red or blue shifts observed in spectral lines by astronomers are due to the Doppler effect. The Doppler effect occurs when an object is moving either towards or away from an observer, causing a shift in the wavelengths of light. In the context of astronomy, the Doppler effect can be used to determine the radial velocities of distant objects, such as stars and quasars.
By measuring the wavelengths of the absorption lines in the spectrum of an object, astronomers can detect the Doppler shift and determine whether the object is moving towards us (blue shift) or away from us (red shift). This information can provide valuable insights into the motion and dynamics of celestial objects in the universe.