An Etymological Dictionary of Astronomy and Astrophysics
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The diffraction effects obtained when either the source of light or observing screen, or both, are at a finite distance from diffracting aperture or obstacle. → Fraunhofer diffraction.

Named after Jean Augustin Fresnel (1788-1827), French physicist, a key figure in establishing the wave theory of light. His earlier work on interference was carried out in ignorance of that of Thomas Young (1773-1829), English physician and physicist, but later they corresponded and were allies; → diffraction.

Any of the four interactions in nature between bodies of matter and that are mediated by one or more particles. Also called the → fundamental force. In order of decreasing strength, the four fundamental interactions are the → strong interaction, the → electromagnetic interaction, the → weak interaction, and the → gravitational interaction.

→ fundamental; → interaction.

The limiting case of → astronomical refraction when the light path is entirely within the Earth's atmosphere.

→ geodetic; → refraction.

The force that pulls material bodies toward one another because of → gravitation.

→ gravitational; → attraction.

Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force.

→ gravitational; → contraction.

Mutual attraction between any two bodies that have mass.

→ gravitational; → interaction.

The angular distance of an object below the horizon when it appears to lie on the horizon.

→ horizontal; → refraction.

Same as → refractive index.

→ index; → refraction.

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.

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.

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.

The decrease in the length of a body moving in the direction of its length as measured by an observer situated in that direction. The shortening factor is [1 - (v/c)²]^1/2, where v is the relative velocity and c light speed.

→ Lorentz; → contraction.

The fractional amount (by mass) of a given → chemical element or → nuclide in a given → chemical composition. In chemical composition studies of astrophysical objects the mass fractions of → hydrogen, → helium, and all the remaining chemical elements are usually denoted by the parameter X, Y, and Z, respectively. Their sum is defined as X + Y + Z = 1. The parameter Z is usually referred to as → heavy elements or → metals.

→ mass; → fraction.

A process in which the energy, composition, or structure of an atomic nucleus changes.

→ nuclear; → reaction.