Chapter 15, Problem 93A

To determine

To Explain: The use of Doppler Effect in the study of astronomy.

The role of Doppler Effect in Big Bang theory, in the detection of planets around other stars and in the study of motions of galaxies.

Explanation of Solution

Introduction:

The frequency of wave varies when the source and observer move towards or away from each other. This effect on frequency is known as Doppler effect.

The Doppler effect occurs for both mechanical and electromagnetic wave motion.

As Doppler Effect occurs in electromagnetic waves, such as light, it is of great use in astronomy as it results in red-shift or blue-shift.

Light is shifted to the red end of the spectrum when the source is moving away from the detector and to the blue end of the spectrum when the source is moving towards the detectors.

As per Big Bang theory, the universe is undergoing expansion, and the Doppler Effectdescribes the redshift. If the universe is a static universe then there should be no shifting at all. The Doppler Effect thus supports Big Bang theory.

Doppler Effect is also effective for objects that are rotating (planets).

The planet emits circularly polarized light, that light’s frequency is shifted. Light gets a Doppler shift in orbital angular momentum simply by scattering off a rotating object. The orbital angular momentum of the planet helps to determine the planet’s rotation.

Astronomers observe light from different galaxies and use Doppler Effect to measure the speed at which stars and galaxies are approach or recede away from the Earth, that is, their radial velocities. The astronomers determine how rapidly stars and galaxies move away from the Earth by calculating the extent to which their light is stretched and shifted to red part of the spectrum (red shift).