Here's why:
* Redshift and the Doppler Effect: Redshift occurs because of the Doppler effect. Imagine an ambulance siren. As the ambulance approaches, the sound waves are compressed, resulting in a higher pitch. As it moves away, the sound waves are stretched, resulting in a lower pitch. Light waves behave similarly. If a celestial object is moving away from Earth, the light waves are stretched, causing a shift towards the red end of the electromagnetic spectrum (hence the name "redshift").
* Redshift and Distance: The amount of redshift is directly proportional to the distance of the object. The farther away an object is, the more its light is stretched, and the greater the redshift. This relationship is known as Hubble's Law.
* Redshift and Velocity: The amount of redshift also indicates the velocity at which the object is moving away from Earth. A larger redshift means a faster recession velocity.
In summary: By measuring the redshift of light from distant objects, astronomers can infer their distance and how fast they are moving away from us. This information is crucial for understanding the expansion of the universe and the evolution of galaxies.
