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Glossary · Galaxies & Cosmology
Redshift
The stretching of light from distant objects, and the universe's odometer.
Light from a receding source arrives with its waves stretched toward the red end of the spectrum. For distant galaxies this is not really motion through space but the expansion of space itself, stretching the light in transit. Because the stretching accumulates with travel time, redshift is a direct measure of how long the light has been flying and therefore how far back you are looking. Astronomers quote it as z: the cosmic microwave background sits at z ≈ 1,100, the most distant galaxies Webb has confirmed are around z = 14, and everything you can see with your eyes is effectively z = 0.
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Related terms
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A millisecond flash of radio energy from another galaxy, cause still unsettled.
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Two good measurements of the universe's expansion rate that stubbornly disagree.
Dark energy
The name for whatever is making the expansion of the universe speed up.
Dark matter
Matter that has gravity but does not interact with light, and outweighs the visible sort five to one.
Questions
What is Redshift?
The stretching of light from distant objects, and the universe's odometer.
Why does it matter?
Because the stretching accumulates with travel time, redshift is a direct measure of how long the light has been flying and therefore how far back you are looking. Astronomers quote it as z: the cosmic microwave background sits at z ≈ 1,100, the most distant galaxies Webb has confirmed are around z = 14, and everything you can see with your eyes is effectively z = 0.