Constants and unit conventions

Constants and unit conventions¶

CODATA 2018 constants in CGS¶

Status: verified

Fundamental and atomic constants are frozen to the versioned CODATA 2018 adjustment and expressed in CGS units.

Scope¶

The CODATA-derived constants in jaxstro.constants, including exact revised-SI constants and explicitly rounded derived compatibility literals.

Conventions¶

• base dimensions are centimetres, grams, and seconds

• CODATA 2018 is intentionally versioned; it is not described as the current adjustment

• A_RAD and R_GAS are stored rounded literals, not bit-identical defining expressions

Sources¶

• source — the versioned values and exactness states of fundamental constants. Locator: NIST CODATA 2018 archive and linked 2018 recommended-values tables

Code & validation¶

• code: src/jaxstro/constants.py::G_CGS

• code: src/jaxstro/constants.py::C_CGS

• code: src/jaxstro/constants.py::H_CGS

• code: src/jaxstro/constants.py::K_B

• code: src/jaxstro/constants.py::A_RAD

• code: src/jaxstro/constants.py::R_GAS

• validation: tests/unit/test_constants.py::TestFundamentalConstants::test_gravitational_constant

• validation: tests/unit/test_constants.py::TestFundamentalConstants::test_speed_of_light

• validation: tests/unit/test_constants.py::TestFundamentalConstants::test_radiation_constant

• validation: tests/unit/test_constants.py::TestElectromagneticAndAtomicConstants::test_molar_gas_constant_from_k_b_n_a

IAU nominal solar conversions and bolometric zero point¶

Status: verified

Exact IAU nominal radius, luminosity, effective temperature, and solar mass parameter are separated from jaxstro’s rounded gram compatibility scale.

Scope¶

RSUN_CM, LSUN_ERG_S, TEFF_SUN, MSUN_G, and the conventionally rounded M_BOL_SUN value.

Conventions¶

• IAU B3 nominal values are exact conversion factors, not measured solar properties

• MSUN_G is a legacy gram compatibility scale derived from nominal (GM)_sun and frozen G

• M_BOL_SUN=4.74 is the rounded value implied by the exact B2 and B3 luminosity scales

Sources¶

• source — R_sun^N, L_sun^N, T_eff,sun^N, and (GM)_sun^N exact values and semantics. Locator: IAU 2015 Resolution B3, nominal solar conversion constants

• source — the exact L_0 luminosity defining M_bol=0. Locator: IAU 2015 Resolution B2, absolute bolometric magnitude zero point

Code & validation¶

• code: src/jaxstro/constants.py::MSUN_G

• code: src/jaxstro/constants.py::RSUN_CM

• code: src/jaxstro/constants.py::LSUN_ERG_S

• code: src/jaxstro/constants.py::TEFF_SUN

• code: src/jaxstro/constants.py::M_BOL_SUN

• validation: tests/unit/test_constants.py::TestSolarParameters::test_solar_mass

• validation: tests/unit/test_constants.py::TestSolarParameters::test_solar_radius

• validation: tests/unit/test_constants.py::TestSolarParameters::test_solar_luminosity

• validation: tests/unit/test_constants.py::TestSolarParameters::test_m_bol_sun_value_and_consistency

CGS-rooted unit systems¶

Status: verified

Every UnitSystem is defined by explicit CGS mass, length, and time scales; gravitational constants are derived dimensionally from the frozen CGS value.

Scope¶

UnitSystem conversion methods, predefined systems, aliases, and DEFAULT_UNITS.

Conventions¶

• DEFAULT_UNITS is CGS in the domain-agnostic foundation package

• G_code = G_CGS M_scale T_scale^2 / L_scale^3

• downstream domain packages own any different default

Sources¶

• source — the audited implementation contract and tested unit-system aliases. Locator: Verified non-defect observations; UnitSystem.G dimensional conversion

Code & validation¶

• code: src/jaxstro/units.py::UnitSystem

• code: src/jaxstro/units.py::DEFAULT

• code: src/jaxstro/__init__.py::DEFAULT_UNITS

• validation: tests/unit/test_units.py::TestDefaultSystem::test_default_is_cgs

• validation: tests/unit/test_units.py::TestGravitationalConstant::test_cgs_g_value

• validation: tests/unit/test_units.py::TestGravitationalConstant::test_stellar_g_value

• validation: tests/unit/test_units.py::TestToFromCGS::test_roundtrip