What this calculator does
Redshift & blueshift works out doppler shift of light and the recession or approach velocity it implies. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
Formulaz = (λobs − λemit) / λemit; relativistic Doppler: 1+z = √((1+β)/(1−β)), β = v/c
The inputs explained
| Field | What to enter |
|---|---|
| Emitted (rest-frame) wavelength (nm) | A number, measured in nm. Starts at 656.3. |
| Observed wavelength (nm) | A number, measured in nm. Starts at 660. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with emitted (rest-frame) wavelength
Every other input is held at the calculator’s starting values while emitted (rest-frame) wavelength varies. Select any row to load that scenario into the calculator.
How the answer changes with emitted (rest-frame) wavelength
| Emitted (rest-frame) wavelength (nm) | Redshift z | Classification | Recession velocity (relativistic) |
|---|---|---|---|
| 328 | 1.012 | Redshift (receding) | 181,037,591 m/s |
| 492 | 0.3415 | Redshift (receding) | 85,618,586 m/s |
| 656 | 0.0061 | Redshift (receding) | 1,822,430 m/s |
| 984 | -0.3293 | Blueshift (approaching) | -113,748,313 m/s |
| 1,313 | -0.4973 | Blueshift (approaching) | -178,852,035 m/s |
| 1,969 | -0.6648 | Blueshift (approaching) | -239,230,024 m/s |