Redshift and Blueshift

Redshift and Blueshift

Subject: Science and Technology

Section: Space Technology

Context:

NASA’s release of five images from the early work of the James Webb Space Telescope grist for further research and Astrophysicist Dipankar Bhattacharya glimpse the origins of life through the ‘eyes’ of the James Webb.

Content:

Significance of James Webb

• Webb is designed to sense IR, which means it can receive radiation from galaxies that have moved very far. Till now it has taken IR of5 microns (wavelength) so far,

but it is designed to go up to 28 microns.

• Unlike other telescopes, the Webb has the capability to penetrate dust clouds and look at newly forming stars. That is how the planetary nebula (catalogued NGC 3132), which is about 2,500 light years away was seen.

About Redshift and Blueshift:

• They describe the change in the frequency of a light wave depending on whether an object is moving towards or away from us.
• When an object is moving away from us, the light from the object is known as redshift, and when an object is moving towards us, the light from the object is known as
• Astronomers use redshift and blueshift to deduce how far an object is away from Earth, the concept is key to charting the universe’s expansion.
• Red shift of 1,100 means that the universe was 1,101 times smaller than now. smaller than now. Similarly, red shift of 20 means, 21 times smaller than now. Thus, the universe began emitting light from the time the red shift was around 20 and before that it was dark(i.e., the universe was just neutral gas, no luminous object).
• The terms redshift and blueshift apply to any part of the electromagnetic spectrum, including radio waves, infrared, ultraviolet, X-rays and gamma rays. So, if radio waves are shifted into the ultraviolet part of the spectrum, they are said to be blue shifted or shifted toward the higher frequencies. Gamma rays shifted to radio waves would mean a shift to a lower frequency or a redshift.
• The concept of redshift and blueshift is closely related to the Doppler effect.
• American astronomer Edwin Hubble was the first to describe the redshift phenomenon and tie it to an expanding universe.
• The redshift of an object is measured by examining the absorption or emission lines in its spectrum. These lines are unique for each element and always have the same spacing.
• At least three types of redshift occur in the universe — from the universe’s expansion, from the movement of galaxies relative to each other and from “gravitational redshift”, which happens when light is shifted due to the massive amount of matter inside of a galaxy.

Other Basic Concepts

Waves and Wavelength

• Electromagnetic waves, which are waves of energy, don’t need any medium to propagate — they originate somewhere, keep radiating through space unless halted by an object, like earth. Higher the energy, the shorter the wavelength.
• Wavelength is the distance between two successive crests of a wave.
• The number of peaks per second is called ‘frequency’.
• So, wavelength and frequency are related — the higher the wavelength, the smaller the frequency.
• Waves are classified according to their wavelength.

Electromagnetic Spectrum

• Electromagnetic waves come in a variety of wavelengths, depending upon their source.
• In the descending order of wavelengths (ascending order of frequencies), they are:
  • Radio waves
  • Microwaves
  • Infra-red or IR (further classified as far, middle and near)
  • Visible light (red, orange, yellow, blue, violet)
  • Ultra-violet
  • X-rays and
  • Gamma rays.

Doppler Effect

• This refers to an apparent shift in soundwave frequency for observers depending on whether the source is approaching or moving away from them.
• This principle applies to light as well as sound.