Physics

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Redshift Calculator.

Calculate measured spectral redshift from rest and observed wavelengths.

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01

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Redshift: 0.1

Redshift

0.000000

Results update automatically as you type.

Use Cases

Astronomy Education

Students and educators can use this calculator to quickly compute redshift values for examples in class, helping to illustrate the Doppler effect and cosmic expansion.

Example: Enter rest wavelength 656.3 nm (as 6.563e-7 m) and observed 700 nm (7e-7 m) to find z ≈ 0.066.

Quick Data Check

Researchers and hobbyists can verify redshift calculations for spectral lines from observational data without manual math.

Example: Check the redshift of a galaxy's H-alpha line by entering the rest and observed wavelengths in meters.

Frequently Asked Questions

What is redshift and how is it calculated?
Redshift (z) is the change in wavelength of light due to the Doppler effect or cosmic expansion. It is calculated as (observed wavelength - rest wavelength) / rest wavelength. This calculator uses the rest and observed wavelengths you provide to compute z.
What units should I use for the wavelengths?
Both rest and observed wavelengths must be entered in meters (m). The calculator expects values in meters, so ensure you convert from nanometers or other units before entering.
Can this calculator determine the velocity of the object?
No, this calculator only computes the redshift z from the given wavelengths. It does not convert redshift to velocity or distance. For velocity, you would need additional formulas and constants.

Tips & Common Mistakes

Tips

  • Ensure both wavelengths are in meters. Convert nanometers to meters by multiplying by 1e-9.
  • Double-check that the observed wavelength is greater than the rest wavelength for a positive redshift (object moving away).
  • If the observed wavelength is less than the rest wavelength, the result will be negative, indicating blueshift.
  • Use scientific notation for very small or large numbers to avoid entry errors.

Common Mistakes to Avoid

  • Entering wavelengths in nanometers instead of meters, leading to incorrect results.
  • Mixing up rest and observed wavelengths, which flips the sign of the redshift.
  • Assuming the calculator provides velocity or distance; it only gives the dimensionless redshift z.

Last updated: August 13, 2026