Redshift Wavelength Calculator

Calculator Inputs

Calculation Mode

Spectral Line Name

Wavelength Unit

Observed Wavelength

Rest Wavelength

Redshift z

Velocity (km/s)

Temperature (K)

Refractive Index

Plotly Graph

Example Data Table

Spectral Line	Rest Wavelength (nm)	Observed Wavelength (nm)	Redshift z	Notes
H-alpha	656.28	700.00	0.06662	Moderate redshift example
Na D	589.00	610.50	0.03650	Shifted absorption line
Custom UV Line	280.00	322.00	0.15000	Higher redshift case
Near IR Line	950.00	1045.00	0.10000	Infrared range example

Formula Used

Redshift from wavelengths: z = (λ_observed − λ_rest) / λ_rest

Observed wavelength: λ_observed = λ_rest × (1 + z)

Rest wavelength: λ_rest = λ_observed / (1 + z)

Frequency: f = c / λ

Photon energy: E = h × f = h × c / λ

Relativistic velocity mode: 1 + z = √[(1 + β) / (1 − β)], where β = v / c

This page also reports shift, frequency change, energy change, wavenumber change, and a simple thermal reference energy from kT.

How to Use This Calculator

Select the calculation mode that matches your known values.
Choose a wavelength unit such as nm, µm, Å, or m.
Enter the observed wavelength, rest wavelength, redshift, or velocity as needed.
Add refractive index and temperature if you want extra context values.
Press Calculate Now to display results above the form.
Review the plotted comparison between rest and observed wavelengths.
Use CSV or PDF buttons to export the calculated output.

FAQs

1. What does redshift wavelength mean?

It describes how much a spectral line moves toward longer wavelengths. A positive shift means the observed wavelength is longer than the rest wavelength.

2. How is redshift z calculated?

Use z = (observed wavelength − rest wavelength) ÷ rest wavelength. The result is dimensionless and compares relative spectral stretching.

3. Can this calculator find observed wavelength directly?

Yes. Select the mode that uses rest wavelength and redshift. The tool multiplies the rest wavelength by (1 + z).

4. Why does the calculator also show frequency and energy?

Wavelength changes affect photon frequency and energy. Longer observed wavelengths correspond to lower frequency and lower photon energy.

5. What is the velocity mode used for?

Velocity mode estimates wavelength shift from relativistic Doppler motion. It is useful when source speed is known instead of z.

6. Which wavelength unit should I choose?

Choose the unit that matches your data source. Nanometers suit visible spectra, angstroms suit line tables, and micrometers suit infrared work.

7. Does refractive index change the vacuum redshift result?

No. The main redshift relation still depends on wavelength ratio. Refractive index here adds medium-based frequency context for comparison.

8. Can I export the results?

Yes. The page includes CSV and PDF export buttons. They package the displayed result values into easy download files.