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◉ Science·2 min·Updated Mar 11, 2026

What is Redshift?

Redshift

Quick Answer

A phenomenon where light from distant objects in space shifts to longer wavelengths, indicating that these objects are moving away from us. This shift helps astronomers understand the universe's expansion and the movement of galaxies.

Overview

Redshift occurs when light emitted from an object in space is stretched as it travels through the universe, resulting in a shift toward the red end of the spectrum. This effect is primarily due to the Doppler effect, which describes how the frequency of waves changes based on the relative motion of the source and observer. When a galaxy moves away from us, the light it emits becomes redshifted, allowing astronomers to measure its speed and distance. Understanding redshift is crucial for astronomers as it provides insights into the universe's expansion. Edwin Hubble first discovered this relationship in the 1920s, leading to the realization that the universe is constantly expanding. By measuring the redshift of various galaxies, scientists can estimate how fast they are moving away from Earth and infer the overall rate of expansion of the universe. A real-world example of redshift can be seen in the light from distant galaxies. For instance, the light from the Andromeda Galaxy, which is moving toward us, exhibits a blueshift, while most other galaxies show redshift due to their distance and speed. This phenomenon not only helps astronomers map the universe but also raises questions about its ultimate fate, such as whether it will continue to expand indefinitely or eventually collapse.

Frequently Asked Questions

Redshift is caused by the relative motion of light-emitting objects moving away from the observer. As these objects move away, the light waves are stretched, leading to a shift toward longer wavelengths.
Astronomers measure redshift by analyzing the light spectrum from distant objects. They look for specific spectral lines and determine how much they have shifted toward the red end of the spectrum, which indicates the object's speed and distance.
Redshift provides evidence for the expansion of the universe, showing that most galaxies are moving away from us. It helps scientists understand the rate of expansion and offers clues about the universe's history and future.