sextant
Enable an agent to recognise a sextant, assess its angular measurement capability and condition, and determine whether and how it can support a reliable observation.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
recalled by Codex without web access - no source was read
Researched by: Codex
Purpose and description
Enable an agent to recognise a sextant, assess its angular measurement capability and condition, and determine whether and how it can support a reliable observation.
A sextant is a graduated double-reflection instrument that measures the angle between two visible directions, especially the altitude of a celestial body above a horizon for celestial navigation.
It can be Determine whether a target pair and angular separation fall within the instrument's usable range.; Bring direct and reflected images into coincidence and record the indicated angle.; Check index error and attach applicable instrument corrections to an observation.; Assess compatibility with a telescope, horizon reference or observation accessory.; Restrict observation when optical protection, alignment or mechanical condition is inadequate.; Select documented cleaning, adjustment or servicing actions and require appropriate checks afterward..
Distinguishing features
A reflecting sextant combines a direct view with a view reflected by an index mirror and horizon mirror so the observer can bring two targets into coincidence.
Its indicated angle follows double-reflection geometry: rotation of the index mirror changes the measured angle by twice that rotation.
The characteristic arc is approximately one sixth of a circle, with a scale representing approximately twice the physical arc angle; actual measuring limits must be recorded separately.
Unlike an octant or reflecting quadrant, its nominal physical arc is about 60 degrees rather than 45 or 90 degrees.
Unlike a theodolite, it ordinarily measures separation through optical coincidence rather than through separate telescope pointings around mounted axes.
Scope
+ Reflecting geometry used to bring two directions into apparent coincidence
+ Frame, graduated arc, index arm, mirrors, telescope and angular readout
+ Instrument errors, adjustment history and measurement uncertainty
+ Interfaces for natural-horizon, artificial-horizon and other angular observations
+ Optical protection, handling, maintenance and readiness for use
- Complete celestial navigation procedures and position-fixing calculations
- Ephemerides, nautical almanacs and astronomical object catalogues
- Chronometers and independent timekeeping systems
- Vessel motion, voyage planning and bridge navigation systems
- Standalone artificial horizons and their internal operation
- Historical astronomical instruments called sextants that do not use the reflecting operating principle
Characteristics
- Sextant sense and variant
- marine reflecting; bubble-equipped; other documented reflecting variant; unresolved Establishes whether the instrument belongs within this model and which observation interfaces apply.
- Angular measuring range
- degrees, with minimum and maximum indicated angles Determines whether a proposed angular separation can be measured.
- Readout arrangement
- vernier; micrometer drum; electronic; other documented arrangement Determines how an observation is read and which readout errors require checking.
- Smallest readable increment
- arcminutes or arcseconds Describes readout resolution without treating it as demonstrated accuracy.
- Index error
- arcminutes, with explicit sign convention, test method and observation date Supports the corresponding correction and reveals changes in zero alignment.
- Calibration evidence
- linked certificate, correction table or documented comparison Connects accuracy claims and angular corrections to evidence for the relevant instrument.
- Horizon mirror configuration
- split field; whole horizon; other documented configuration Affects target acquisition and the visibility of the two images.
- Viewing optics
- magnification in ×; objective aperture in mm; field of view in degrees Helps judge suitability for target brightness, acquisition and image alignment.
- Horizon reference
- natural horizon; external artificial horizon; integrated bubble reference; no horizon required for the selected observation Determines what the measured angle represents and which observation corrections may apply.
- Optical and mechanical readiness
- unchecked; serviceable for specified use; restricted; requires adjustment; requires repair Prevents an apparently readable instrument from being assumed fit for observation.
- Solar observation protection
- absent; unverified; damaged; documented suitable protection installed Solar viewing requires suitable protection supported by evidence rather than inferred from apparent darkness.
- Power dependency
- none for angular measurement; illumination supply; electronic readout supply; other documented dependency Separates passive optical operation from optional functions that depend on power.
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.sextant-artifact
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 16 findings · 26 questions.
Identity and measuring envelope Establishes which sense of sextant is represented and which angular tasks it supports.
The name alone does not establish reflecting geometry, variant or usable angular range.
Instrument boundary
Separates reflecting sextants from related instruments and historical namesakes.
Reflecting sextant identity
Recognition depends on the optical arrangement and arc geometry, with uncertain namesakes held for scope review.
- Does the instrument combine direct and doubly reflected sight lines through a movable index mirror? definition
- What evidence distinguishes it from an octant, reflecting quadrant or non-reflecting astronomical sextant? boundary
Angular capability
Records the usable angular envelope independently of the nominal arc name.
Range and readability
Scale limits and readable increments constrain observations but do not establish accuracy.
- What are the minimum and maximum readable angles, including any extension beyond zero or the nominal range? measurement
- What increment can be read using the installed vernier, micrometer or electronic readout? measurement
Optical coincidence and controls Describes how the instrument forms, aligns and reads two target images.
A sextant's usefulness depends on image coincidence and index-arm control working together.
Image paths
Identifies the mirrors and viewing optics used to combine the target directions.
Direct and reflected visibility
Mirror configuration and telescope properties affect whether both targets can be acquired and aligned.
- Which horizon mirror configuration is fitted, and how are the direct and reflected fields presented? definition
- What telescope magnification, aperture and field of view are documented for the installed optics? measurement
Index arm operation
Connects coarse movement, fine adjustment and readout to the measured angle.
Movement and reading integrity
The arm, clamp and fine adjustment must support repeatable image coincidence and an unambiguous reading.
- How are coarse movement, clamping and fine adjustment performed on this sextant design? action
- Does approaching the same angle from opposite directions reveal backlash, sticking or a change in the indicated reading? measurement
Instrument errors and evidence Separates alignment checks, instrument corrections and demonstrated measurement quality.
Optical coincidence can produce a plausible reading even when instrument errors remain.
Alignment and zero
Covers index error and alignment of mirrors and the viewing axis.
Alignment check record
A useful check records the method, conditions and result rather than merely labelling the instrument adjusted.
- What index error was measured, by which method and under which sign convention? measurement
- Which documented checks address index-mirror perpendicularity, horizon-mirror side error and telescope collimation where applicable? action
Accuracy and corrections
Links accuracy claims and angle-dependent corrections to their evidential limits.
Supported angular performance
Resolution, repeatability and accuracy require distinct records; correction evidence must match the instrument and its condition.
- Which calibration or comparison supports the claimed accuracy across the usable arc? provenance
- What uncertainty remains after applicable instrument corrections, and which effects were excluded from that assessment? measurement
Observation reference and record Makes each angular observation interpretable through its targets, reference and correction status.
The same sextant reading can represent different quantities depending on the horizon arrangement and selected target contact.
Target and horizon reference
Identifies the two observed directions and how a horizon reference is supplied.
Observation geometry
Natural-horizon, reflected artificial-horizon, bubble-reference and target-to-target observations require explicit distinctions.
- Which two directions are brought into coincidence, including the selected limb or centre of an extended target? definition
- Does the horizon arrangement produce an altitude reading, a doubled altitude angle or another angular separation? boundary
Reading to observation handoff
Separates the instrument reading from subsequent navigation or surveying reductions.
Interpretable observation record
The raw reading and correction status remain available alongside the contextual records needed by the consuming task.
- Are the raw reading, applied index correction and any other instrument corrections recorded separately? measurement
- Which linked records must supply observation time, eye height, atmospheric conditions or other inputs required by the intended reduction? boundary
Protection and serviceability Assesses solar-viewing protection and the condition of sensitive optical and mechanical parts.
Damaged shades can endanger the observer, while shock, corrosion and optical deterioration can invalidate measurements.
Solar viewing protection
Requires evidence that the installed protection is suitable for the actual solar observation configuration.
Verified solar configuration
Shade presence or apparent darkness alone does not establish suitability for direct solar observation.
- What manufacturer documentation or applicable test evidence establishes the suitability of the installed solar shades? provenance
- What observation restriction applies if a required shade is missing, damaged, loose or unverified? action
Handling and restoration
Connects condition findings and handling events to maintenance and renewed measurement checks.
Return to observation readiness
Service decisions consider mirror coatings, shade mounts, frame integrity, index movement and any powered accessories.
- What evidence of impact, frame distortion, corrosion, coating damage or impaired index movement limits use? measurement
- Which documented cleaning, repair or adjustment actions are appropriate, and which alignment or calibration checks must follow? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Check these first
Recalled without web access and unsourced; every item is a lead to verify.
- This describes the instrument class, not a particular manufacturer's model or individual unit.
- Listed kinds overlap: a bubble sextant is an artificial-horizon implementation.
- Measuring range, resolution and accuracy depend on the model; graduation size is not a guarantee of measurement accuracy. No specific governing standard is asserted from recall.
- Which of these check these first hold for the sense of sextant this model covers, and on what evidence? provenance
Kinds and varieties
Recalled without web access and unsourced; every item is a lead to verify.
- Marine sextant
- Bubble sextant
- Artificial-horizon sextant
- Which of these kinds and varieties hold for the sense of sextant this model covers, and on what evidence? provenance
Real-world use
Recalled without web access and unsourced; every item is a lead to verify.
- Measuring solar or stellar altitude for celestial navigation when combined with observation time, almanac data and sight reduction.
- Providing a navigation method independent of satellite positioning.
- Measuring horizontal angles between landmarks for coastal position fixing.
- Teaching celestial navigation and practical angular measurement.
- Which of these real-world use hold for the sense of sextant this model covers, and on what evidence? provenance
Typical measurements
Recalled without web access and unsourced; every item is a lead to verify.
- Physical extent of the nominal graduated arc - Approximately 60 - degree
- Nominal angular measuring span through double reflection - Approximately 120 - degree
- Micrometer drum graduation on many marine sextants - 1 - arcminute
- Which of these typical measurements hold for the sense of sextant this model covers, and on what evidence? provenance
Failure modes and hazards
Recalled without web access and unsourced; every item is a lead to verify.
- Index error and mirror misalignment introduce systematic angular errors.
- Frame distortion, impact damage or wear can impair calibration and repeatability.
- Corrosion, dirty optics or damaged mirror coatings reduce image quality.
- Direct solar observation without appropriate intact sextant shades can cause permanent eye injury.
- Horizon misidentification, vessel motion and incorrect observation time or altitude corrections can produce substantial position errors.
- Which of these failure modes and hazards hold for the sense of sextant this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Recalled without web access and unsourced; every item is a lead to verify.
- Octant - Uses a nominal 45-degree arc to measure angles through approximately 90 degrees; a sextant uses a nominal 60-degree arc for approximately 120 degrees.
- Theodolite - Measures horizontal and vertical angles using a mounted telescope and graduated circles rather than bringing two images into coincidence through double reflection.
- Sextant observation - An observation is a measurement event and its recorded result; the sextant is the physical instrument.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of sextant this model covers, and on what evidence? provenance
What the second pass must settle
- Does the registry intend sextant to include historical non-reflecting astronomical instruments, or only the reflecting navigational family?
- Which issuing bodies and current standards, if any, govern sextant performance, calibration and solar-shade suitability for the intended applications?
- What sourced ranges for dimensions, mass, angular coverage and accuracy are representative of marine, training and bubble-equipped variants?
- Which adjustment procedures are appropriate for users, and which require specialist service for each design?
- Does an existing Vercy world model already cover this concept and require the registry entry to link to it instead of receiving a separate publication?