An Etymological Dictionary of Astronomy and Astrophysics
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A binary star system in which mass transfer between the components takes place. → contact binary; → Roche lobe.

Interacting, adj. of → interact; → binary.

Galaxies that are close enough for their mutual gravitational attraction to produce perturbed shapes or extruded filaments of stellar material, called → tidal tails. Most galaxies are in clusters, and gravitational interactions between them are common.

Interacting, adj. of → interact; → galaxy.

General: Mutual or reciprocal action or influence.
Physics: 1) What happens between a system and its surroundings when an observable change in one corresponds to or correlates with an observable change in the other.
2) The natural phenomenon of the transfer of energy between two particles. The four known kinds of interactions, in the order of increasing strength, are: → gravitational, → weak, → electromagnetic, and → strong.

Interaction, from → inter-; + → action.

Capable of acting on or influencing each other

From → interaction; + → -al.

1) Acting one upon or with the other.
2) Computers: Of or pertaining to a system or program that maintains an exchange with the user, alternately accepting input and then responding.

→ inter-; → active.

Of, existing, or occurring in the space between galaxies. → intergalactic absorption, → intergalactic cloud, → intergalactic matter , → intergalactic medium , → warm-hot intergalactic medium.

→ inter-; → galactic.

→ Absorption features in the spectra of bright sources like → quasars attributed to a tenuous matter filling the medium between galaxies.

→ intergalactic; → absorption.

→ Intergalactic matter in the form of clouds.

→ intergalactic; → cloud.

Very low density material found indirectly in the space between galaxies. → intergalactic absorption.

→ intergalactic; → matter.

The matter or environment between the galaxies of a → cluster.

→ intergalactic; → medium.

A quantity used in studies of → emission nebulae to convert the → ionic abundance of a given chemical element to its total → elemental abundance. The elemental abundance of an element relative to hydrogen is given by the sum of abundances of all its ions. In practice, not all the ionization stages are observed. One must therefore correct for unobserved stages using ICFs. A common way to do this was to rely on → ionization potential considerations. However, → photoionization models show that such simple relations do not necessarily hold. Hence, ICFs based on grids of photoionization models are more reliable. Nevertheless here also care should be taken for several reasons: the atomic physics is not well known yet, the ionization structure of a nebula depends on the spectral energy distribution of the stellar radiation field, which differs from one model to another, and the density structure of real nebulae is more complicated than that of idealized models (see, e.g., Stasińska, 2002, astro-ph/0207500, and references therein).

→ ionization; → correction; → factor.

A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical  → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.

→ isotope; → fractionation

Same as → isotope fractionation.

→ isotopic; → fractionation

The contraction of a volume of gas under its → gravity, accompanied by the → radiation of the lost → potential energy as → heat.

After the Scottish physicist William Thomson, also known as Lord Kelvin (1824-1907) and the German physicist and physician Hermann Ludwig Ferdinand von Helmholtz (1821-1894), who made important contributions to the thermodynamics of gaseous systems; → contraction.

The constant of proportionality relating the separations of lines of successive pairs of adjacent components of the levels of a spectral multiplet to the larger of the two J-values for the respective pairs. The interval between two successive components J and J + 1 is proportional to J + 1.

After Alfred Landé (1888-1976), a German-American physicist, known for his contributions to quantum theory; → facteur.

Same as → fourth contact at an eclipse.

→ last; → contact.

One of the two laws governing → refraction of light when it enters another transparent medium: a) The → incident ray, normal to the surface, and refracted ray, all lie in the same plane. b) → Snell's law is satisfied.

→ law; → refraction.

Same as → Lorentz contraction.

→ length; → contraction.

Of a force, the straight line along which the force → vector is directed. The action of a force on a → rigid body does not change when its point of application is displaced along the line of action. Hence, forces applied to a rigid body can be regarded as non-localized, or sliding, vectors.

→ line; → action.

1) The act or process of liquefying or making liquid.
2) The state of being liquefied.

→ liquefy; → -tion.