Chapter 23, Problem 1GST

To determine

The star, by referring the given spectra representing four identical stars in a galaxy. When one star is not moving relative to the observer, another is moving away from observer, and two stars are moving towards the observer.

Answer to Problem 1GST

The movement of four identical stars by referring the given spectra is as follows:

• Star A is moving away from the observer because the overall shift is towards the end of the absorption line spectrum.
• Star B is not moving relative to the observer.
• Stars C and D are moving towards the observer because both A and B have shifted towards the blue end of the absorption line spectrum.

Explanation of Solution

The Doppler effect is the variation in wavelength or frequency of a wave for an observer who is moving relative to the wave source.

The Doppler Effect for stars is observed by comparing the lines in the absorption spectrum; the shifting of spectral lines towards the long end of the electromagnetic spectrum is known as redshift and this indicates that the star is moving away from the observer.

The shifting of spectral lines towards the short end of electromagnetic spectrum indicates that the star is moving towards the observer. The amount of shifting gives information about the speed at which the object is moving (either towards or away from the observer).