An Etymological Dictionary of Astronomy and Astrophysics
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A → structure formation scenario in which small galaxies form first, and larger structures are then formed in due course. Contrary to → top-down structure formation.

→ bottom; → up; → structure; → formation; → galaxy.

In → special relativity, the causal relationship between → events involving a → light cone.

→ causal; → structure.

The geometric framework to which a crystal may be referred and the arrangement of atoms or electron density distribution relative to that framework, usually determined by X-ray diffraction measurements.

→ crystal; → structure.

An arrangement and interrelationship of parts that is of → crystalline nature.

→ crystalline; → structure.

A → method or → format for organizing and storing data. Any data structure is designed to organize data to suit a specific purpose so that it can be accessed and worked with in appropriate ways. In computer programming, a data structure may be selected or designed to store data for the purpose of working on it with various algorithms.

→ data; → structure.

Closely spaced components seen at high resolution in a → spectral line. The phenomenon is explained by the fact that instead of a single → energy level corresponding to a given value of the → quantum number  n, there are actually a number of energy levels lying close to one another. → fine-structure constant, → fine-structure line.

→ fine; → structure.

A measure of the strength of → interaction between a → charged particle and the → electromagnetic field. It is a → dimensionless number expressed (in → cgs units) by α = e²/ħc, where e is the → electron charge, ħ is the → reduced Planck's constant, and c is the → speed of light. It is approximately equal to 1/137 or 7.3 × 10^-3. The smallness of this number is of great importance since it determines the size of → atoms and the → stability of → matter. Same as → electromagnetic coupling constant.

→ fine structure; → constant.

A → spectral line whose → energy levels have a → fine structure. Examples are [C II] 157.7 μm (→ singly ionized carbon), [O III] 88 μm, and [Ne II] 12.8 μm.

→ fine; → structure; → line.

A → hierarchial structure that can be likened to fractals.

→ fractal; → structure

The global shape and the arrangement of the various parts or constituents of a galaxy.

→ galactic; → structure.

A cosmological → structure formation model in which the smallest gravitationally bound structures (→ quasars and galaxies) form first, followed by → groups, → galaxy clusters, and → superclusters of galaxies.

→ hierarchical; → structure; → formation.

In spectroscopy, the → splitting of a spectral line into a number of very thin components. It results from a small perturbation in the energy levels of atoms or molecules due to the magnetic dipole-dipole interaction arising from the interaction of the nuclear → magnetic moment with the → spin of the electron. It can be observed only at high spectral dispersion. → fine structure.

→ hyperfine; → structure.

The physical characteristics of that part of a star lying below the → photosphere. More specifically, the study of its various zones (→ core, → convective zone, → radiative zone) and the transfer of energy through them.

→ internal; → structure; → star.

The distribution of galaxies and other forms of mass on large distance scales, covering hundreds of millions of → light-years.

→ large; → scale; → structure.

Same as → Dyson sphere.

→ mega-; → structure.

Crystalline arrangement in which equivalent positions are not necessarily occupied by atoms of a single kind.

→ random; → structure.

A type of data structure in which data are represented as tables in which no entry contains more than one value.

→ relational; → data; → structure.

The morphology of a galaxy which displays → spiral arms.

→ spiral; → structure.

A physical model that describes the internal arrangement of a star in detail and makes detailed predictions about the luminosity, the color, and the future evolution of the star.

→ stellar; → structure.

A set of → differential equations describing the physical properties of stars based on two main assumptions: a star is a perfect sphere and the net force on a macroscopic mass element is zero. If the effects of rotation and magnetism are ignored, these assumptions lead to a set of five differential equations.

→ stellar; → structure; → equation.