Concept · beginner
Redshift
A stretching of light toward longer wavelengths as the universe expands, used to measure cosmic distance and look-back time.
What redshift means
When light from a distant galaxy travels across an expanding universe, its wavelength stretches. Astronomers call this redshift.
Higher redshift means the light left earlier and traveled farther. That is why Webb's infrared vision matters: highly redshifted ultraviolet and optical light from early galaxies arrives on Earth as infrared.
Why it matters for discoveries
A single redshift estimate helps answer:
- How far away is this galaxy?
- How old was the universe when the light left?
- Is the object unexpectedly bright or massive for that era?