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Showing 1621–1650 of 1709 reference entries

Chemistry · PhysicsIntensive, extensive, specific and molar properties

Scaling the system amount is different from changing its state.

DefinitionChemistry · MeasurementRelative atomic mass and isotope composition

Relative atomic mass is dimensionless and depends on the isotope composition being averaged.

DefinitionChemistry · MeasurementMolar mass and mass–amount conversion

Molar mass converts a specified substance's amount into mass.

DefinitionChemistry · MeasurementAmount concentration, molality and composition fractions

Concentration must declare its numerator and denominator.

DefinitionChemistryDilution conserves the retained solute amount

Dilution arithmetic refers to final solution volume, not the amount of solvent poured in.

MethodChemistryLimiting reagent, theoretical yield and percent yield

Stoichiometry gives a maximum under a specified reaction model; recovery measures the actual yield.

MethodChemistryFormal charge is equal-share electron accounting

Formal charge, oxidation state and partial charge answer different questions.

DefinitionChemistryElectrolyte strength, solubility and concentration

Strong describes ion formation by dissolved solute, not how much solute dissolves.

DefinitionChemistryComplete ionic and net ionic equations

Cancel unchanged species while conserving both atoms and charge.

MethodBiology · ChemistryWater polarity and biological interactions

Water's molecular interactions help explain solvation, cohesion and thermal buffering.

Empirical findingBiologyCell size and surface-to-volume scaling

For geometrically similar cells, volume grows faster than surface area.

ModelBiology · ChemistryOsmolarity and tonicity

Total particle concentration and lasting cell-volume effect are different properties.

DefinitionBiologyChromosome sets and DNA content

DNA replication doubles DNA content without doubling chromosome-set ploidy.

DefinitionBiologyOrganisms, populations, communities and ecosystems

Ecological levels describe different interacting sets and environments.

DefinitionBiologyPopulation size, density and demographic balance

Total individuals and individuals per area or volume must be distinguished.

ModelBiologyMutation and selection: different roles

Mutations do not generally appear because an organism needs their future advantage.

Empirical findingBiologyClades and rooted-tree interpretation

Shared ancestry is represented by topology, not by the left-to-right order of tips.

MethodBiology · ChemistryPlant water potential and pressure balance

Osmotic and mechanical contributions together determine passive water movement.

ModelEarth & cosmosRock and mineral are different material categories

A mineral species and a rock aggregate have different identifying features.

DefinitionEarth & cosmosEarth's compositional and mechanical layers

Crust–mantle–core and lithosphere–asthenosphere partition Earth by different properties.

ModelEarth & cosmos · MeasurementGeodetic latitude, longitude and reference systems

A coordinate pair needs a reference surface, origin and convention.

DefinitionEarth & cosmos · MeasurementMap projections and distortion

Flattening Earth's curved reference surface requires a choice of distortions.

ModelEarth & cosmos · MeasurementEllipsoid height, geoid and orthometric height

Height above a geometric reference is not automatically height above a gravity reference.

DefinitionEarth & cosmosRotation, axial tilt and seasonal sunlight

Axial tilt changes the angle and duration of sunlight in opposite hemispheres.

ModelEarth & cosmosNatural hazard and disaster risk

A harmful physical process and the potential losses it creates are different quantities.

DefinitionEarth & cosmosUsing present processes to infer Earth's past

Modern process evidence informs geological interpretation only with the past boundary conditions.

MethodEarth & cosmosLunar phases and synchronous rotation

Phases change the visible illuminated fraction; they are not Earth's shadow moving across the Moon.

ModelEarth & cosmosSolar and lunar eclipse geometry

New or full Moon is necessary for the corresponding eclipse but does not guarantee alignment.

ModelEarth & cosmosIAU Solar-System body categories

A scoped naming convention distinguishes planets, dwarf planets, small bodies and satellites.

DefinitionEarth & cosmos · MeasurementAstronomical unit and light-year

The astronomical unit and light-year measure lengths, with different defining conventions.

Definition
DefinitionSource checked

Astronomical unit and light-year

Earth & cosmosMeasurement

The astronomical unit and light-year measure lengths, with different defining conventions.

Key knowledge

The astronomical unit, symbol au, is exactly 149597870700 metres; it is a fixed length, not the changing instantaneous Earth–Sun separation. A light-year is the distance light travels in vacuum in a year, approximately 9.46 × 10^15 metres. It measures length, not elapsed time; precise conversion must specify the year convention.

Conditions and scope

  • The au value is the convention adopted by IAU in 2012 and recorded by BIPM; the light-year value here is rounded.
  • For cosmological sources, choosing a length unit does not choose between luminosity, angular-diameter or other model-dependent distance measures.
Sources · 2

References

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

  1. SI Brochure, ninth edition, version 4.01: mole, mass constants and accepted non-SI unitsBIPMReference guide · PDFbipm.orgRead source
  2. What is a light-year?NASA ScienceReference guidescience.nasa.govRead source

Evidence and review

Inspected SI Brochure printed pp.140–141 Table 8 and note (j) for exact au, and NASA's light-year distance definition/rounded conversion. No exact Julian-year conversion, current object-distance catalogue or historical AU measurement claim is asserted.

2026-10-10 · Independent Mathematics and Information editor (/root/core_math_information). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.

Related reference entries

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Scientific relationships · 2 / 2

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

  1. Uses definition
    Relationship sources · 2

    Linked statements

    • The astronomical unit, symbol au, is exactly 149597870700 metres; it is a fixed length, not the changing instantaneous Earth–Sun separation. A light-year is the distance light travels in vacuum in a year, approximately 9.46 × 10^15 metres. It measures length, not elapsed time; precise conversion must specify the year convention.

    A light-year converts a specified year-duration to vacuum-light path length using the vacuum speed of light.

  2. Related to
    Relationship sources · 2

    Linked statements

    • The astronomical unit, symbol au, is exactly 149597870700 metres; it is a fixed length, not the changing instantaneous Earth–Sun separation. A light-year is the distance light travels in vacuum in a year, approximately 9.46 × 10^15 metres. It measures length, not elapsed time; precise conversion must specify the year convention.

    Astronomical length units are used to report distances; they do not themselves provide the parallax inference or its validity conditions.

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