Redshift

Definition of Redshift

  • Redshift is a phenomenon in physics where the electromagnetic radiation, like light, from an object undergoes an increase in wavelength.
  • It is referred to as ‘red’ shift because the shift is towards the longer wavelength (lower frequency) end of the spectrum, which is coloured red.
  • The redshift of a distant galaxy or quasar is measured by examining the spectral lines in its spectrum.

The Causes and Examples of Redshift

  • The main cause of redshift is the expansion of the Universe. When light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum, that means the object is moving away from the observer.
  • Another cause of redshift is the gravity of a massive object, which can cause the observed light to be ‘stretched’, increasing the wavelength and causing the light to shift to the red end of the spectrum.
  • Examples of redshift include the light from distant galaxies moving away from the Milky Way due to the expansion of the universe, and light from stars orbiting close to a black hole.

The Importance of Redshift

  • Redshift is crucial to astronomy because it helps scientists estimate how far away a star or galaxy is and its movement speed.
  • It was the observation of redshifted galaxies that led to the realization that the Universe is expanding, a key piece of evidence for the Big Bang theory.
  • Studying redshift also helps astronomers determine the properties of dark matter and dark energy, two of the most mysterious components of the Universe.

Measuring Redshift

  • Redshift is measured using spectroscopy. The spectral lines of elements in a star’s light (a form of electromagnetic radiation) are identified and their displacement from their normal positions are measured.
  • The greater the displacement of these spectral lines, the higher the redshift, and thus the faster the object is moving away.
  • The Doppler Effect is used to calculate the velocity at which a star or galaxy is moving away. The formula to calculate this based on redshift is v = c * z, where v is velocity, c is the speed of light, and z is the redshift.