Question

Please explain carefully (that is, design experiments that exploit the Doppler effect) how one could show that the Earth rotates on its axis and revolves around the sun.

Answer 1

The Doppler effect is basically measured in the frequency of the signals received by ground receiving stations when tracking spacecraft around the earth. The increasing or decreasing distances between the spacecraft and the ground station may be caused by a combination of the spacecraft's trajectory, its orbit around a planet, Earth's revolution about the sun, and Earth's daily rotation on its axis. A spacecraft approaching Earth will add a positive frequency bias to the received signal(Doppler Effect). However, if it flies by Earth, the received Doppler bias will become zero as it passes Earth, and then become negative as the spacecraft moves away from Earth(Doppler Effect).

The Earth's daily rotation adds a positive frequency bias to the received signal as the spacecraft rises in the east at a particular tracking station, and it adds a negative frequency bias to the received signal as the spacecraft sets in the west.

The Earth's revolution about the sun adds a positive frequency bias to the received signal during that portion of the year when the Earth is moving toward the spacecraft, and it adds a negative frequency bias during the part of the year when the Earth is moving away. So from here, we can conclude that the Doppler Effect is able to recognize the motion of the earth around the sun and about its own axis.

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