Redshift z
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The redshift (z) calculation is critical in cosmology to measure the universe's expansion. It compares the observed wavelength (λ_obs) with the emitted wavelength (λ_emit) using the formula z = (λ_obs − λ_emit)/λ_emit. Positive z values indicate a light source moving away from the observer, commonly observed in distant galaxies due to cosmic expansion.
This calculator is used in observational astronomy and cosmological research. To use it, input λ_obs and λ_emit in consistent units (nanometers or meters). The result, z, helps determine the recession velocity (as a fraction of light speed) of celestial objects like galaxies or quasars, and estimates cosmic distances.
It applies to phenomena such as expanding galaxies, supernovae, and cosmic microwave background. However, it's essential to ensure wavelengths are accurately measured, excluding other shift causes (like relativistic Doppler effects). Negative z values, called blueshift, indicate the object is approaching the observer.
Common precautions include unit verification, observational data precision, and understanding this is a linear approximation. For velocities near light speed, more complex relativistic corrections are required.
Frequently asked questions
What is redshift z?
Redshift z measures how light from distant objects stretches due to the universe's expansion. Positive values indicate movement away, negative (blueshift) indicate movement toward the observer.
How does the calculator work?
It uses the formula z = (λ_obs − λ_emit)/λ_emit, requiring observed and emitted wavelengths in identical units to compute the shift.
When should I use it?
For studying expanding galaxies, supernovae, or cosmic microwave background, where universal expansion affects light wavelengths.
What units should I use?
Use nanometers, meters, or consistent units for λ_obs and λ_emit. Avoid mixing scales.
What does a negative result mean?
A negative z (blueshift) means the object is approaching, common in stars or galaxies moving toward the observer.