Introduction to Redshift

Relative increase in wavelength of electromagnetic radiation in the emission spectrum of astronomical objects.

Redshift is a fundamental concept in astronomy and cosmology, playing a crucial role in our understanding of the universe. This unit will provide an introduction to redshift, its historical background, and its relationship with the Doppler Effect.

Definition of Redshift

Redshift is a phenomenon where light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum. In layman's terms, redshift happens when light from an object that is moving away from the observer is perceived as being shifted towards the red end of the visible light spectrum.

Historical Background: Discovery and Early Studies

The concept of redshift was first proposed by Christian Doppler in the 19th century, who suggested that the frequency of light and sound waves changes if the source of these waves is moving relative to the observer. This became known as the Doppler Effect.

In the early 20th century, astronomer Vesto Slipher observed the redshift of spectral lines in the light from galaxies, providing the first empirical evidence for the expansion of the universe. Later, Edwin Hubble's observations confirmed that galaxies were indeed moving away from us, and the farther they were, the faster they were moving. This led to the formulation of Hubble's Law, which states that the velocity of a galaxy is directly proportional to its distance from us.

Understanding the Doppler Effect and its Relation to Redshift

The Doppler Effect refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

In the context of light from celestial bodies, when a star or galaxy is moving away from an observer, the light's wavelength appears longer, i.e., it shifts towards the red end of the spectrum. This is known as redshift. Conversely, if the star or galaxy is moving towards the observer, the light's wavelength appears shorter, or blueshifted.

In conclusion, redshift is a key concept in astronomy and cosmology, providing critical evidence for the expansion of the universe. By understanding redshift and the Doppler Effect, we can measure the velocities of celestial bodies and estimate their distances, contributing to our understanding of the universe's structure and evolution.