Description
Calculate a small-redshift-offset velocity approximation under supplied conventions.
Cosmological quantities depend on scale factor, redshift, distance definition and the dimensionless Hubble parameter h. Proper and comoving distances differ at a specified epoch, and h-scaled units differ from the dimensional Hubble constant. A scalar rescaling or model contribution preserves supplied conventions without fitting a cosmology or inferring an observed distance.
Calculate a small-redshift-offset velocity approximation under supplied conventions.
When to use this tool
Use Redshift Velocity Small Offset Convention when you already have redshiftOffset, referenceRedshift, suppliedLightSpeed and need to calculate a small-redshift-offset velocity approximation under supplied conventions.
How to use the tool and how it works
- Enter redshiftOffset, referenceRedshift, suppliedLightSpeed. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read approximateVelocity. Use the output convention below.
Require referenceRedshift>-1 and suppliedLightSpeed positive/finite; return suppliedLightSpeed*redshiftOffset/(1+referenceRedshift).1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| redshiftOffset | Redshift Offset | Required. Finite number. |
| referenceRedshift | Reference Redshift | Required. Finite number; strictly above -1. |
| suppliedLightSpeed | Positive speed in the desired output velocity unit. | Required. Finite number; strictly above 0. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| approximateVelocity | suppliedLightSpeed*redshiftOffset/(1+referenceRedshift); a local small-offset convention, not a general recession velocity. | Required. Finite number. |
{
"input": {
"redshiftOffset": 0.001,
"referenceRedshift": 1,
"suppliedLightSpeed": 300000
},
"output": {
"approximateVelocity": 150
}
}Limitations and assumptions
- The output uses the supplied speed unit. This is a local offset approximation, not general recession velocity, a full relativistic Doppler conversion or a peculiar-velocity measurement.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use the complete cosmological model and its parameter, epoch and unit definitions for a physical inference. Review redshift, distance, lensing and spectrum conventions before combining these local terms; they do not perform line-of-sight integration, parameter estimation or uncertainty analysis.
References
Similar or alternative tools
- Cosmological Time Dilation Interval Pair
Apply a supplied cosmological redshift time-dilation factor.
- Cosmological Simulation Snapshot Scale Tag
Label a simulation snapshot's supplied scale factor and corresponding redshift.