Air Mass sec(z) Plane-Parallel Approximation Calculator
Named plane-parallel sec(z) relative airmass bounded 0..75°, not near-horizon curved-atmosphere Kasten Young. Caller independently establishes frames, units, epoch, covariance and instrument context; not an identity, association or astrometric quality certification.
Description
Plane-parallel airmass increases with the secant of zenith angle.
Plane-parallel airmass increases with the secant of zenith angle.1
The approximation loses suitability near the horizon and omits atmospheric curvature and refraction. Use Air Mass sec(z) Plane-Parallel Approximation Calculator to evaluate the supplied inputs under the model explained below.
When to use Air Mass sec(z) Plane-Parallel Approximation Calculator
Use Air Mass sec(z) Plane-Parallel Approximation Calculator to evaluate the supplied inputs under the model explained below. Establish the units, measurement scope and model assumptions before entering values.
How to use Air Mass sec(z) Plane-Parallel Approximation Calculator and understand its results
- Establish the units, measurement scope and model assumptions before entering values.
- Enter Zenith angle degrees using the field table and validation rules below, then run the tool.
- Read Plane parallel airmass; interpret the units, signs, ordering and unknown-value placeholders described below.
- Correct reported input errors and rerun. Apply successful results according to their specific meanings and check the assumptions before using them in a decision.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| zenithAngleDegrees | Zenith angle degrees | number | Required; constraints below |
Enter zenith angle from 0 to 75 degrees inclusively. Return 1/cos(angle) as dimensionless plane-parallel airmass. Zenith gives 1; angles beyond the bound fail. No horizon extension, spherical atmosphere or refraction is added.
airmass=sec(zenithAngle) Use the field order, units and branch conditions described above.
| Output field | Meaning | Value type |
|---|---|---|
| planeParallelAirmass | Plane parallel airmass | number |
{
"input": {
"zenithAngleDegrees": 60
},
"output": {
"planeParallelAirmass": 1.9999999999999996
}
}Limitations and assumptions
The approximation loses suitability near the horizon and omits atmospheric curvature and refraction. Apply the exact scope and assumptions explained above.
All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse arrays fail validation. Domain-specific bounds, alignments and supported tokens are explained above; extremely large inputs or outputs can also be rejected. Input errors differ from successful false results, empty match lists and unknown-evidence placeholders.
Alternative or Complementary methods
Use Atmospheric Extinction mag/Airmass for a related task: Extinction can be compared across airmasses with a band-specific coefficient.
Use Star Count Limiting Magnitude Band for a related task: Visible-star counts depend on a defined sky sample and limiting-magnitude observations.
References
Similar or alternative tools
- Atmospheric Extinction mag/Airmass
Extinction can be compared across airmasses with a band-specific coefficient.
- Star Count Limiting Magnitude Band
Visible-star counts depend on a defined sky sample and limiting-magnitude observations.