Right ascension, declination and reference epochs
Celestial angular coordinates require a declared reference system and date conventions.
Key knowledge
In equatorial sky coordinates, declination is angular position north or south of the reference equatorial plane; right ascension is measured eastward around that plane from a specified zero direction. The traditional zero uses the northward equinox crossing, but modern reference systems can fix axes independently of Earth's instantaneous equator and equinox. Catalog positions also have a reference epoch, with proper motions used to propagate changing directions. These two angles specify direction, not distance.
Conditions and scope
- State the reference system, origin, epoch and whether coordinates are catalog, geocentric or topocentric apparent positions before comparing them.
- A fixed reference orientation does not make every object's coordinates constant. Transformation to an observer's horizon requires time, location and appropriate models.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Equatorial angular definitions, traditional equinox versus modern reference axes, catalog epoch and proper-motion dependence.
2026-10-10 · Independent Mathematics and Information editor (AI editorial/source review; not the Chemistry/Biology/Earth author). The specified introductory inventory has no unresolved demonstrated material gap after the changes and body-based reuse. Existing advanced references retain their historical scoped approvals. English-only reference prose and explicit Lithuanian-translation-pending status are preserved.
Foundational review
2026-10-10 · Independent AI editorial inspection of this new compact reference entry, its equations, applicability, sources and knowledge connections.
Sources from other places
Agreement within this scope
Shared equatorial frames, time-dependent reference orientation and proper motion.
Catalogue directions need a reference frame and epoch.
Basílio X. Santiago / Universidade Federal do Rio Grande do Sul
- FIS02014: Um pouco sobre Astrometria BrazilPortuguese
§1 Introduction, p1; §2 reference frames, pp2–4; §3 Parallaxes and proper motions, pp4–6
- FIS02014: Um pouco sobre Astrometria
Entry details
Permanent link to this entry ↗- Record identity
- foundation-cosmos-equatorial-coordinates
- Revision
- foundations-audit.1
- Structured reference record
- Foundational core completion