Kasten Young Optical Airmass
Evaluate Kasten–Young relative optical air mass for apparent altitude above the horizon; this is an atmospheric model approximation.
Description
Relative optical air mass approximates the longer atmospheric path away from the zenith.
Relative optical air mass approximates the longer atmospheric path away from the zenith. The Kasten–Young relation modifies a simple secant near the horizon.1
Evaluate Kasten–Young relative optical air mass for apparent altitude above the horizon; this is an atmospheric model approximation.
When to use Kasten Young Optical Airmass
Use this tool to evaluate Kasten–Young relative optical air mass for apparent altitude above the horizon; this is an atmospheric model approximation.
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 Kasten Young Optical Airmass 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 altitudeDegrees using the field table and calculation rules, then run the tool.
- Read relativeAirmass. 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 |
|---|---|---|---|
| altitudeDegrees | Altitude degrees | number | Required |
Enter apparent altitude from 0 through 90 degrees. The tool converts the sine argument to radians, evaluates the empirical relation and returns dimensionless relative air mass. The horizon is accepted; below-horizon values are errors.
airmass=1/[sin(altitude)+0.50572(altitude+6.07995)^(-1.6364)] Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| relativeAirmass | Relative airmass | number |
{
"input": {
"altitudeDegrees": 30
},
"output": {
"relativeAirmass": 1.9942928525292503
}
}Limitations and assumptions
This is an atmospheric model approximation, not an extinction correction or weather measurement. It requires apparent altitude rather than automatically adding refraction to a geometric altitude.
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 Bennett Observed Altitude Refraction: Apply Bennett refraction to observed altitude, with caller pressure and temperature; anomalous atmospheric structure is not modeled. For a complementary task, use Equatorial Horizontal Coordinates: Transform geometric hour angle and declination to altitude and azimuth north-through-east; no refraction or time-to-hour-angle conversion is inferred.
References
-
Kasten Young Optical Airmass — tool.io
Similar or alternative tools
- Bennett Observed Altitude Refraction
Apply Bennett refraction to observed altitude, with caller pressure and temperature; anomalous atmospheric structure is not modeled.
- Equatorial Horizontal Coordinates
Transform geometric hour angle and declination to altitude and azimuth north-through-east; no refraction or time-to-hour-angle conversion is inferred.