Bennett Observed Altitude Refraction
Apply Bennett refraction to observed altitude, with caller pressure and temperature; anomalous atmospheric structure is not modeled.
Description
Atmospheric refraction raises observed altitude relative to geometric altitude.
Atmospheric refraction raises observed altitude relative to geometric altitude. The Bennett approximation used here takes observed altitude and supplied pressure/temperature to estimate the correction.1
Apply Bennett refraction to observed altitude, with caller pressure and temperature; anomalous atmospheric structure is not modeled.
When to use Bennett Observed Altitude Refraction
Use this tool to apply Bennett refraction to observed altitude, with caller pressure and temperature; anomalous atmospheric structure is not modeled.
Prepare the source, detector or coordinate measurements. Confirm frame, epoch, angular units, axis directions and the stated RA proper-motion convention before entering values.
How to use Bennett Observed Altitude Refraction and understand its results
- Prepare the source, detector or coordinate measurements. Confirm frame, epoch, angular units, axis directions and the stated RA proper-motion convention before entering values.
- Enter observedAltitudeDegrees, pressureHpa, temperatureC using the field table and calculation rules, then run the tool.
- Read refractionArcminutes, trueAltitudeDegrees. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| observedAltitudeDegrees | Observed altitude degrees | number | Required |
| pressureHpa | Pressure hPa | number | Required |
| temperatureC | Temperature c | number | Required |
Enter observed altitude 0–90 degrees, nonnegative pressure hPa and temperature strictly above −273°C. The tool applies the formula in degree arguments, forces refraction to zero at 90 degrees, and returns arcminutes plus observed-minus-refraction true altitude. Zero pressure gives zero correction.
Rarcmin=max(0,cot[h+7.31/(h+4.4)])(pressure/1010)283/(273+temperature) Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| refractionArcminutes | Refraction arcminutes | number |
| trueAltitudeDegrees | True altitude degrees | number |
{
"input": {
"observedAltitudeDegrees": 45,
"pressureHpa": 1010,
"temperatureC": 10
},
"output": {
"refractionArcminutes": 0.9948479678568615,
"trueAltitudeDegrees": 44.98341920053572
}
}Limitations and assumptions
This is an atmospheric approximation without anomalous structure or near-horizon ray tracing. It does not accept a geometric altitude as though it were observed or provide uncertainty bounds; the formula uses 273, not an implicit replacement constant.
Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.
Alternative or Complementary methods
Use Kasten Young Optical Airmass: Evaluate Kasten–Young relative optical air mass for apparent altitude above the horizon; this is an atmospheric model approximation. For a complementary task, use Differential Atmospheric Dispersion: Compute signed first-order atmospheric differential refraction from caller-supplied wavelength-dependent indices at actual conditions; near-horizon curvature is excluded.
References
-
Bennett Observed Altitude Refraction — tool.io
Similar or alternative tools
- Kasten Young Optical Airmass
Evaluate Kasten–Young relative optical air mass for apparent altitude above the horizon; this is an atmospheric model approximation.
- Differential Atmospheric Dispersion
Compute signed first-order atmospheric differential refraction from caller-supplied wavelength-dependent indices at actual conditions; near-horizon curvature is excluded.