Occultation Stellar Angular Diameter
Estimate diameter from a central occultation-edge crossing and shadow speed, then angular size; diffraction, integration smearing and noncentral chords are excluded.
Description
A central occultation-edge crossing can relate duration to a projected stellar diameter.
A central occultation-edge crossing can relate duration to a projected stellar diameter. Dividing that scale by the supplied stellar distance gives a geometric angular-diameter estimate.1
Estimate diameter from a central occultation-edge crossing and shadow speed, then angular size; diffraction, integration smearing and noncentral chords are excluded.
When to use Occultation Stellar Angular Diameter
Use this tool to estimate diameter from a central occultation-edge crossing and shadow speed, then angular size; diffraction, integration smearing and noncentral chords are excluded.
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 Occultation Stellar Angular Diameter 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 diameterCrossingSeconds, shadowKmPerSecond, stellarDistanceKm using the field table and calculation rules, then run the tool.
- Read projectedDiameterKm, angularDiameterMilliarcseconds. 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 |
|---|---|---|---|
| diameterCrossingSeconds | Diameter crossing seconds | number | Required |
| shadowKmPerSecond | Shadow km per second | number | Required |
| stellarDistanceKm | Stellar distance km | number | Required |
Enter positive crossing seconds, shadow speed km/s and stellar distance km. Return projected diameter km and angular diameter milliarcseconds using radians-to-degrees conversion. The crossing time must describe the modeled diameter rather than an arbitrary event interval.
diameter=duration × shadowSpeed; angularDiameter=2atan(diameter/(2distance)) Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| projectedDiameterKm | Projected diameter km | number |
| angularDiameterMilliarcseconds | Angular diameter milliarcseconds | number |
{
"input": {
"diameterCrossingSeconds": 0.01,
"shadowKmPerSecond": 10,
"stellarDistanceKm": 1000
},
"output": {
"projectedDiameterKm": 0.1,
"angularDiameterMilliarcseconds": 20626.480607520905
}
}Limitations and assumptions
Diffraction, finite integration, limb structure and noncentral chords are excluded. This does not fit a light curve or infer shadow speed and distance.
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 Occultation Step Candidates: Find discrete sampled flux-drop candidates at a supplied threshold; two steps are not by themselves evidence for an occulted binary. For a complementary task, use Angular Projected Binary Separation: Convert angular binary separation and distance to a tangent-plane projected separation in AU; this is not a deprojected semimajor axis.
References
-
Occultation Stellar Angular Diameter — tool.io
Similar or alternative tools
- Occultation Step Candidates
Find discrete sampled flux-drop candidates at a supplied threshold; two steps are not by themselves evidence for an occulted binary.
- Angular Projected Binary Separation
Convert angular binary separation and distance to a tangent-plane projected separation in AU; this is not a deprojected semimajor axis.