[OU.03] A star is moving away from Earth. An astronomer plans to measure the distance of the star from Earth by observing the blue shift in its spectrum. Which of these statements best explains why the astronomer's method of measuring the star distance is inappropriate? The spectral shift of moving stars cannot be observed. Common instruments cannot measure the blue shift accurately. A blue shift can be observed when the star moves towards Earth. Rate of motion of stars cannot be matched with the rate of measuring distances.

The correct option is;

A blue shift can be observed when the star moves towards Earth

Explanation:

For a star moving away from an observer, the wavelength of the light emitted by the star becomes (shifts) longer and the light is seen to shift towards the longer red end of the spectrum of light

When the the star moves towards the observer, the light is seen to have shorter wavelength such that the light is observed to move towards the blue (shorter wavelength) end of the spectrum of light

Therefore, the astronomer, will rather observe a redshift for the receding star

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