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Showing 1681–1709 of 1709 reference entries

Measurement · PhysicsRadiant flux, intensity, irradiance, exitance and radiance

Optical power, directional power and surface densities are different quantities.

DefinitionMeasurement · PhysicsPhotometric weighting, lumen, candela, lux and luminance

Photometry weights radiation with a specified standard visual response.

DefinitionMeasurementWriting SI quantities and unit symbols

Symbol form, spacing and parentheses preserve the meaning of reported quantities.

DefinitionMeasurementGram prefixes and the kilogram exception

Mass prefixes attach to gram even though kilogram is the SI base unit.

DefinitionMeasurementRounding a result with its uncertainty

Report useful digits without treating extra digits as proof of accuracy.

MethodMeasurement · Physics · ChemistryCommon non-SI units and exact SI conversions

Common non-SI unit names require their correct SI scale factors.

DefinitionPhysics · ChemistryGas pressure as molecular momentum transfer

Molecular collisions link macroscopic pressure to random translational motion.

ModelChemistry · PhysicsOrdinary aggregate states and bulk behavior

Solid, liquid and gas describe bulk behavior rather than chemical identity.

ModelChemistryInferring empirical and molecular formulas from composition

Element mass ratios become atom ratios through molar masses, with uncertainty and sample identity retained.

MethodChemistryLewis structures and valence-electron accounting

A Lewis diagram accounts for bonding and nonbonding valence electrons in a specified connectivity.

MethodChemistryElectron-domain geometry and molecular shape

VSEPR distinguishes the arrangement of electron regions from the positions of atoms.

ModelChemistryElectronegativity, bond polarity and molecular polarity

Polar bonds can cancel in a molecule; molecular geometry matters.

ModelChemistrySolutions, solutes, solvents and solvation

Dissolution disperses specified molecular or ionic species in a solvent.

DefinitionChemistrySolubility, saturation and supersaturation

A saturation limit is an equilibrium property under specified conditions, not a synonym for concentration.

DefinitionChemistryFiltration separates retained solids from a fluid

Ordinary filtration separates undissolved particles; dissolved species can remain in the filtrate.

MethodChemistryDistillation and vapor–liquid composition

Distillation uses vapor–liquid partitioning and condensation, with a limit at an azeotrope.

MethodBiologyGene, allele, genotype and phenotype

Genomic sequence variants and observable traits describe different levels of biological information.

DefinitionBiology · ChemistryEnzyme substrates, active sites and induced fit

Substrate recognition and catalysis depend on a dynamic molecular environment.

ModelBiology · ChemistryMonomers, polymers and hydrolysis

Covalent subunit linkage and water-assisted cleavage explain biological polymer structure.

DefinitionBiology · ChemistrySugars, glycosidic linkages and polysaccharides

Sugar connectivity distinguishes energy-storage and structural polysaccharides.

DefinitionBiology · ChemistryFatty acids, storage lipids and membrane lipids

Lipids include several architectures rather than one repeating-monomer polymer class.

DefinitionBiology · ChemistryAmino-acid residues and peptide linkages

The peptide backbone and variable side chains are different parts of protein structure.

DefinitionBiology · ChemistryNucleotides and DNA/RNA backbone polarity

Bases carry sequence information on a chemically directional sugar–phosphate backbone.

DefinitionBiologyCell membrane, cell wall, cytosol and compartments

A cell's boundary, fluid interior and specialized structures have different roles.

DefinitionEarth & cosmos · MeasurementEarthquake location, source magnitude and local intensity

A source location or magnitude does not describe the shaking experienced at every site.

DefinitionEarth & cosmosAtmospheric composition and thermal layers

Composition and temperature structure describe different features of Earth's atmosphere.

ModelEarth & cosmosDrainage basins, outlets and water divides

Surface drainage boundaries depend on the chosen outlet and need not bound groundwater flow.

DefinitionEarth & cosmosThe celestial sphere and the observer's sky

A sky direction is an angular observation, not an object's three-dimensional distance.

ModelEarth & cosmos · MeasurementRight ascension, declination and reference epochs

Celestial angular coordinates require a declared reference system and date conventions.

Definition
ModelSource checked

The celestial sphere and the observer's sky

Earth & cosmos

A sky direction is an angular observation, not an object's three-dimensional distance.

Key knowledge

The celestial sphere is an imaginary surface for representing directions to objects that actually lie at different distances. An observer's zenith is directly overhead and the horizon bounds the local sky. Earth's rotation produces the dominant daily apparent rotation of the sky about the celestial poles; the celestial equator projects Earth's equatorial plane. Which directions rise, set or remain circumpolar depends on observer latitude. Objects can also change direction through their own motion and Earth's orbital motion.

Conditions and scope

  • The sphere is a direction model, not a physical shell or a claim that all stars share one distance.
  • Visibility also depends on obstruction, atmospheric refraction and illumination. Daily apparent rotation is not the entire motion of every sky object.
Sources · 2

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. Astronomy (2016), §2.1 The sky aboveAndrew Fraknoi, David Morrison and Sidney C. Wolff · OpenStax/Rice UniversityTextbook chapteropenstax.orgRead source
  2. COSMOS: Celestial SphereSwinburne University of TechnologyReference guideastronomy.swin.edu.auRead source

Evidence and review

Observer horizon/zenith, projected equator/poles and latitude-dependent apparent sky motion.

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

Fictitious sky-direction sphere, horizon, zenith, poles and equator.

Sky direction is distinct from the distance to an object.

  • Swinburne University of Technology

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–3 of 3 relationships

Scientific relationships · 3 / 3

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 1

    Linked statements

    • The celestial sphere is an imaginary surface for representing directions to objects that actually lie at different distances. An observer's zenith is directly overhead and the horizon bounds the local sky. Earth's rotation produces the dominant daily apparent rotation of the sky about the celestial poles; the celestial equator projects Earth's equatorial plane. Which directions rise, set or remain circumpolar depends on observer latitude. Objects can also change direction through their own motion and Earth's orbital motion.

    Earth's rotation and orbital geometry change the apparent observer sky and Sun's annual direction.

  2. Related to
    Relationship sources · 1

    Linked statements

    • The celestial sphere is an imaginary surface for representing directions to objects that actually lie at different distances. An observer's zenith is directly overhead and the horizon bounds the local sky. Earth's rotation produces the dominant daily apparent rotation of the sky about the celestial poles; the celestial equator projects Earth's equatorial plane. Which directions rise, set or remain circumpolar depends on observer latitude. Objects can also change direction through their own motion and Earth's orbital motion.

    Angular direction alone supplies no distance; parallax uses changes in direction from a known baseline.

  3. Uses definition
    Relationship sources · 1

    Linked statements

    • 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.

    Right ascension and declination specify a direction using a declared celestial reference plane and origin.

Entry detailsPermanent link to this entry ↗
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foundation-cosmos-celestial-sphere
Revision
foundations-audit.1
Structured reference record
Foundational core completion