What does a positive z mean?

A positive z means the observed wavelength is longer than the rest wavelength (redshifted), indicating the source is moving away from the observer.

What does a negative z mean?

A negative z means blueshift — the observed wavelength is shorter than the rest wavelength, indicating the source is moving toward the observer.

Redshift Calculator

Calculate the redshift value (z) of light from a distant object by comparing its observed wavelength to its known rest (laboratory) wavelength. Redshift reveals how fast an object is moving away from us and, at cosmic scales, how the universe is expanding.

Inputs

Results

Redshift (z): 0.00046

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Formula

z = (Observed Wavelength − Rest Wavelength) / Rest Wavelength

Learn How This Works

Astronomy Fundamentals: Parallax, Redshift, and Albedo

Stellar parallax distance, redshift, albedo, and centripetal acceleration — four calculations covering how astronomers measure distance, motion, and reflectivity.

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