Compute the observed frequency from source frequency, relative velocity and the speed of light, using the non-relativistic approximation.
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Optical Doppler shift (non-relativistic) | f' = f (1 ± v/c), first-order approximation for v << c | Classical Doppler effect (Doppler, 1842) |
| Relativistic exact form | f' = f·sqrt((1−β)/(1+β)) for recession, β=v/c | Special relativity (Einstein, 1905) |
Constants used on this page and their authoritative sources, for verification and citation
| Constant | Value | Unit | Source |
|---|---|---|---|
| Speed of light in vacuum c | 299 792 458 | m·s⁻¹ | SI defining constant (exact; this page uses 3×10⁸ as an approximation) |
Note: this page uses the classical longitudinal approximation f′ = f·(1 ± v/c), valid only for v ≪ c. At high speeds use the relativistic form f′ = f·√((1+β)/(1−β)) with β = v/c; transverse motion gives rise to the transverse Doppler effect.