How to use the redshift calculator
Compute redshift from observed and emitted wavelength. Enter emitted wavelength, observed wavelength in the fields above; the redshift z, approx. velocity are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- le — Emitted wavelength (nm)
- lo — Observed wavelength (nm)
Worked example
With emitted wavelength = 656.3 nm, observed wavelength = 670 nm, the calculator gives redshift z ≈ 0.0208746; approx. velocity ≈ 6,258.048 km/s.
Frequently asked questions
What is the formula for the redshift calculation?
Redshift z = (lo-le) / le. Approx. velocity (km/s) = [Redshift z] × 299792.458. Here le is emitted wavelength (nm), lo is observed wavelength (nm).
What inputs do I need for the redshift calculator?
You need emitted wavelength in nm, observed wavelength in nm. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.