Which of these methods involves the observation of red shift and blue shift to measure accurately the distance from earth to the stars?
a) blue shift
b) hr diagram
c) doppler effect
d) parallax method

The correct answer is C. The Doppler Effect involves the observation of red shift and blue shift to measure accurately the distance from Earth to the stars.

Explanation:

The Doppler effect, named after the Austrian physicist Christian Andreas Doppler, is the change in apparent frequency of a wave produced by the relative movement of the source with respect to its observer.

In the case of the visible spectrum of electromagnetic radiation, if the object moves away, its light shifts to longer wavelengths, producing a shift towards red. If the object approaches, its light has a shorter wavelength, moving towards blue. This deviation to red or blue is very slight even at high speeds, such as relative speeds between stars or between galaxies, and the human eye cannot capture it, only measure it indirectly using precision instruments such as spectrometers. If the emitting object moved to significant fractions of the speed of light, the wavelength variation would be directly visible.

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