Question

Explain the Doppler method that astronomers use to search for other planetary systems that orbit a star.

Answer 1

If an object is revolving around a star, its movement will decide the frequency reflected from it due to Doppler Shift.

When the object is moving towards the observer, the Doppler upshifted frequency detected by the observer will be: and when the object is moving away from the observer, the detected frequency will be

For a planet which is revolving around a star, the signal received by the observer will have both these frequency peaks in a given time (in the period of revolution of the planet) and so the presence of both will indicate that a planet exists near the star.