An Etymological Dictionary of Astronomy and Astrophysics
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1) Mental capacity or endowment.
2) Mental capacity or endowment (Dictionary.com).

→ mental; → -ity.

In a star, nebula, or galaxy, the proportion of the material that is made up of → metals, that is elements heavier than → helium. It is generally denoted by Z. The term "metallicity" is a misnomer used in astrophysics.
1) In practice, the metallicity of stars is usually expressed by the number ratio of → iron atoms to → hydrogen atoms per unit volume, with respect to the solar values: [Fe/H] = log₁₀(N_Fe/N_H)_star - log₁₀(N_Fe/N_H)_Sun, where N_Fe and N_H are the numbers of iron and hydrogen atoms per unit volume. In fact it is taken to be equal to the iron → abundance with respect to the solar value. The solar logarithmic iron abundance is 7.50 ± 0.04 (Asplund et al. 2009, ARAA 47, 481), with respect to that of hydrogen which, by convention, is 12.00. Stellar metallicity is often expressed in mass fraction. See also → solar metallicity.
2) Nebular metallicity is often defined as the relative abundance of → oxygen: (N_O/N_H)_neb/(N_O/N_H)_Sun, where N_O and N_H represent the numbers of oxygen and hydrogen atoms per unit volume.

From metallic, from → metal + → -ity.

A plot representing the number of stars (or systems) per metallicity interval, usually expressed in [Fe/H] (abundance of → iron relative to → hydrogen).

→ metallicity; → distribution; → function.

The decrease in the → abundances of → heavy elements in a → disk galaxy as a function of distance from the center. Radial metallicity gradients are observed in many galaxies, including the → Milky Way and other galaxies of the → Local Group. In the case of the Milky Way, several objects can be used to determine the gradients: → H II regions, → B stars, → Cepheids, → open clusters, and → planetary nebulae. The main diagnostic elements are oxygen, sulphur, neon, and argon in photoionized nebulae, and iron and other elements in Cepheids, open clusters, and stars. Cepheids are probably the most accurate indicators of abundance gradients in the Milky Way. They are bright enough to be observed at large distances, so that accurate distances and spectroscopic abundances of several elements can be obtained. Average abundance gradients are generally between -0.03 → dex/kpc and -0.10 dex/kpc, with a a flattening out of the gradients at large galactocentric distances (≥ 10 kpc). The existence of these gradients offers the opportunity to test models of → chemical evolution of galaxies and stellar → nucleosynthesis.

→ metallicity; → gradient.

The state or condition where the force of → gravity is very weak, e.g. the → weightlessness experienced inside an orbiting spacecraft.

→ micro-; → gravity.

The smaller number, part, or quantity of a whole.

→ minor; → -ity.

The quality or state of being → modal.

→ modal; → -ity.

1) The quality of being → modern.
2) A rather diffuse term with many meanings depending on the disciplinary context. Generally, modernity refers to the cultural, intellectual, and economic consequences of the → Enlightenment and the epoch with which they are associated. Modernity is the end result of the → modernization process.

→ modern + → -ity.

Same as → shear modulus.

→ modulus; → rigidity.

The → heat capacity of one → mole of substance: C_μ = μ C, where μ is the → molecular weight and C the → specific heat capacity. The molar heat capacity of water is practically 18 cal/mole.C°.

Molar, adj. of → mole; → heat; → capacity.

The ability of a molecular entity to be distorted from its normal shape by an external → electric field. When a molecule is subjected to an electric field there is a small displacement of electrical centers which induces a dipole in the molecule. More specifically, the molecular polarizability α is defined as the ratio of the induced → dipole moment (p) to the local electric field (E) that produces this dipole moment: α = p/E (in cgse units).

→ molecular; → polaizable; → -ity.

The sum of → absorption coefficient (κ_ν) and → scattering coefficient (σ_ν) at a given frequency: k_ν = κ_ν + σ_ν. See also the → Rosseland mean opacity.

→ monochromatic; → opacity.

An observationally determined relationship between the → morphological classification of galaxies and the → environments in which they are located. Specifically, the morphology-density relation indicates that early-type galaxies (→ ETG) are preferentially located in high density environments, whereas late-type galaxies (→ LTG) are preferentially found in low density environments. Hence, spiral galaxies are rare in the high densities of clusters and are common in the lower density group environments. Early-type galaxies, on the other hand, are common in clusters and are rarely found in isolation.

→ morphology; → density; → relation.

The number which when used as the multiplier of another number leaves the second unchanged; one.

→ multiplicative; → identity.

1) The state of being multiple, made of several components.
2) In atomic and nuclear physics, the number of → levels into which the energy of an atom, molecule, or nucleus splits as a result of → Russell-Saunders coupling between → orbital angular momentum and → spin angular momentum. It is given by 2S+1, where S is the total electron → spin quantum number. The multiplicity of an energy level is indicated by a left superscript to the value of L, where L is the resultant electron orbital angular momentum of the individual electron orbital angular momenta.
3) In → statistical mechanics, the number of → microstates corresponding to a given → macrostate.

→ multiple; → -ity.

The conductivity in a semiconductor caused by a flow of electrons, whereas p-type conductivity is caused by a flow of holes.

n standing for → negative; → type; → conductivity.

A singularity that is not surrounded by an event horizon. It will therefore be visible and communicable to the outside world.

→ naked; → singularity.

The interior of the → nose. It is the structure which extends from the external opening, the → nostrils, to the → pharynx, where it joins the respiratory system.

→ nasal; → cavity.

1) National status; specifically: a legal relationship involving allegiance on the part of an individual and usually protection on the part of the state b : membership in a particular nation.
2) Membership in a particular nation (Merriam-Webster.com).

→ national; → -ity.

1) A nebulous form, shape, or mass.
2) The state or condition of being nebulous.
3) A fuzzy celestial object, constituted of gas and dust, generally part of a larger → nebula.

→ nebulous; → -ity.