Description
Return a transverse comoving size from an angular extent.
Cosmology uses several distance measures and often expresses the expansion rate in mixed astronomical units. Scale-factor relations, inverse-Hubble scales and relativistic velocity composition answer different questions; units and the distinction between local algebra and an integrated expansion history are essential.
Return a transverse comoving size from an angular extent.
When to use this tool
Use Angular Comoving Scale Factor when checking one explicit cosmological distance, redshift-factor or unit convention.
How to use the tool and how it works
- Enter angleRadians, transverseComovingDistance. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read transverseComovingSize. Use the output convention below.
Return a transverse comoving size from an angular extent. Require nonnegative angleRadians and transverseComovingDistance; size = angleRadians*distance.1
Cosmological distance, volume and lookback-time relations require the appropriate expansion-rate and distance conventions; local factors do not replace integration.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| angleRadians | Angle Radians | Required. Finite number; minimum 0. |
| transverseComovingDistance | Transverse Comoving Distance | Required. Finite number; minimum 0. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| transverseComovingSize | Transverse Comoving Size | Required. Finite number. |
{
"input": {
"angleRadians": 0.001,
"transverseComovingDistance": 1000
},
"output": {
"transverseComovingSize": 1
}
}Limitations and assumptions
- Angle must be radians and distance the transverse comoving distance; this is not proper size at redshift or a chord calculation.
- 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 a complete cosmological distance/time calculation and the appropriate observation model when an actual source distance, age or velocity is required.
References
-
Calculation and input contract: cosmology/angular-comoving-scale-factor — tool.io
-
Distance measures in cosmology — David W. Hogg
Similar or alternative tools
- Luminosity Angular Distance Duality Residual
Return a distance-duality residual.
- Distance Modulus Hubble Rescale Term
Rescale a distance modulus under inverse-Hubble distance scaling.