Micrometer Double Star Offsets
Calibrate and rotate micrometer offsets, reporting double-star separation and position angle east of north.
Description
Micrometer measurements need a scale and orientation before their divisions become sky offsets.
Micrometer measurements need a scale and orientation before their divisions become sky offsets. Position angle for a double star is measured east of north rather than from the horizontal detector axis.1
Calibrate and rotate micrometer offsets, reporting double-star separation and position angle east of north.
When to use Micrometer Double Star Offsets
Use this tool to calibrate and rotate micrometer offsets, reporting double-star separation and position angle east of north.
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 Micrometer Double Star Offsets 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 eastDivisions, northDivisions, arcsecondsPerDivision, instrumentRotationDegrees using the field table and calculation rules, then run the tool.
- Read eastOffsetArcseconds, northOffsetArcseconds, separationArcseconds, positionAngleDegrees. 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 |
|---|---|---|---|
| eastDivisions | East divisions | number | Required |
| northDivisions | North divisions | number | Required |
| arcsecondsPerDivision | Arcseconds per division | number | Required |
| instrumentRotationDegrees | Instrument rotation degrees | number | Required |
Enter finite signed division offsets, positive arcseconds/division and instrument rotation degrees. The tool rotates the calibrated pair, returns east/north arcsecond offsets and separation, then wraps atan2(east,north) to [0,360) degrees. Zero combined offset is rejected because direction is undefined.
(east,north)=rotation(angle) × scale × (eastDivisions,northDivisions) Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| eastOffsetArcseconds | East offset arcseconds | number |
| northOffsetArcseconds | North offset arcseconds | number |
| separationArcseconds | Separation arcseconds | number |
| positionAngleDegrees | Position angle degrees | number |
{
"input": {
"eastDivisions": 3,
"northDivisions": 4,
"arcsecondsPerDivision": 0.1,
"instrumentRotationDegrees": 0
},
"output": {
"eastOffsetArcseconds": 0.30000000000000004,
"northOffsetArcseconds": 0.4,
"separationArcseconds": 0.5,
"positionAngleDegrees": 36.86989764584405
}
}Limitations and assumptions
Scale and rotation are supplied calibration values. Distortion, alignment error and uncertainty are not assessed, and the planar offset approximation is not a general spherical-coordinate conversion.
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 Spherical Pair Separation Angle: Compute robust great-circle separation and first-to-second position angle east of north, rejecting directionally undefined coincident/antipodal pairs. For a complementary task, use Cd Matrix Image Axis Angles: Infer both image-axis angles in the WCS tangent plane from CD columns, exposing skew rather than assuming an orthogonal scalar rotation.
References
-
Micrometer Double Star Offsets — tool.io
Similar or alternative tools
- Spherical Pair Separation Angle
Compute robust great-circle separation and first-to-second position angle east of north, rejecting directionally undefined coincident/antipodal pairs.
- Cd Matrix Image Axis Angles
Infer both image-axis angles in the WCS tangent plane from CD columns, exposing skew rather than assuming an orthogonal scalar rotation.