How to Calculate Redshift
What is Redshift?
Redshift (z) measures wavelength increase due to cosmic expansion or relative motion. Higher z indicates greater distance or recession speed.
Formula
Calculate z = (λ_obs - λ_rest) / λ_rest
- z
- (λ_obs - λ_rest) / λ_rest — (λ_obs - λ_rest) / λ_rest
Step-by-Step Guide
- 1Input observed and rest wavelengths
- 2Calculate z = (λ_obs - λ_rest) / λ_rest
- 3Estimate distance using Hubble constant
Worked Examples
Input
z = 0.1
Result
Recession velocity ~10,000 km/s, distance ~400 Mpc
Using H₀ = 70 km/s/Mpc
Common Mistakes to Avoid
- ✕Confusing Doppler redshift with cosmological redshift
- ✕Using non-relativistic formulas for high z
Frequently Asked Questions
Does redshift mean object moving away?
Usually yes, but expansion also redshifts distant objects even in static space.
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