Foundations

For a spherical quasistatic Newtonian star, enclosed mass increases with shell volume and density, while the pressure gradient balances gravity due to enclosed mass.

In an optically thick stellar region close to local thermodynamic equilibrium, radiative diffusion relates luminosity to the temperature gradient through density and an appropriate mean opacity.

A stellar shell's luminosity divergence accounts for local energy production, change in specific internal energy and compression or expansion work.

A displaced parcel that adjusts pressure rapidly but exchanges little heat can continue rising when it becomes less dense than its environment.

The proton–proton chains and CNO cycles convert hydrogen into helium through different reaction sequences; CNO nuclei participate in a catalytic cycle.

An HR diagram compares luminosity with effective temperature or a related spectral classification.

A resolved relative orbit and period can constrain a binary's total mass through Newtonian two-body dynamics.

Cold dense regions of molecular clouds can contract gravitationally when support is insufficient.

Terrestrial planets are dominated by rock and metal; giant planets contain larger proportions of light gases and volatile-rich material.

Atmospheric mass, composition and opacity affect a planet's surface conditions.

Asteroids include bodies with differing rocky, carbon-rich and metallic material signatures; meteorites and spacecraft observations test interpretations of their histories.

The interstellar medium contains ionized, atomic and molecular gas alongside dust.

The Milky Way contains disk, bulge and halo components with differing distributions, motions and stellar populations.

Spiral galaxies commonly contain a disk, bulge and spiral patterns with gas and ongoing star formation.

A thin gravitational lens relates a source's unlensed angular position to observed image positions through a mass-dependent deflection.

In an FLRW expansion model, light emitted and observed by comoving observers is stretched by the ratio of their scale factors.

The hot expanding universe passed through changing particle and radiation conditions.

In the standard cosmological model, small density variations grow gravitationally and dark-matter structures help concentrate baryonic matter after photon coupling becomes less effective.

The Calvin–Benson cycle carboxylates ribulose-1,5-bisphosphate through RuBisCO, reduces the resulting carbon compounds using ATP and NADPH, and regenerates the acceptor.

Nitrogen fixation converts N₂ toward biologically usable reduced nitrogen; ammonification, nitrification and denitrification transform nitrogen among distinct chemical pools.

Stress describes force per area on a specified plane; strain describes deformation.

Fold geometry includes limbs, hinge/axis and axial surface; antiform/synform describe shape while anticline/syncline also depend on stratigraphic order.

Strike is the bearing of a horizontal line in a plane; dip is the maximum inclination from horizontal, perpendicular to strike, with direction specified.

Superposition constrains age order in an undisturbed depositional sequence; inclusions predate their host, and cross-cutting features postdate what they cut.

Fossil assemblages can constrain relative age and depositional environment through observed succession and known ecological context.

Grain size, sorting, sedimentary structures, composition and fossils together constrain depositional processes and environments.

Isostasy describes buoyancy-related balance of lithospheric columns over a deformable mantle in an appropriate model.

Silicate structures organize silicon–oxygen tetrahedra as isolated units, chains, sheets or frameworks.

Rock can begin melting without every component entering the liquid.

Crystallizing minerals remove selected chemical components from a melt.