🔭 Redshift Calculator
Calculate the redshift (z) of light from an astronomical object and the recession velocity it implies.
What redshift measures
Redshift describes how much the wavelength of light from a distant object has stretched compared to its original, emitted wavelength. A positive redshift (z > 0) means the object is moving away from us and its light has shifted toward longer, redder wavelengths; a negative value (blueshift) means it is approaching.
The formula
Redshift is calculated as z = (λ_observed − λ_emitted) / λ_emitted. For low redshifts, recession velocity is approximately v = z × c, where c is the speed of light. This calculator also shows the relativistic Doppler velocity, v = c × [((1+z)² − 1) / ((1+z)² + 1)], which stays valid closer to the speed of light, though at cosmological distances redshift is caused by the expansion of space itself rather than simple relative motion.
This tool uses simplified special-relativistic and Doppler approximations for general educational purposes and is not a substitute for full cosmological modeling.