An Etymological Dictionary of Astronomy and Astrophysics
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An obsolete theory of combustion in which all flammable objects were supposed to contain a substance called → phlogiston, which was released when the object burned. The existence of this hypothetical substance was proposed in 1669 by Johann Becher, who called it terra pinguis "fat earth." For example, as wood burns it releases phlogiston into the air, leaving ash behind. Ash was therefore wood minus phlogiston. In the early 18th century Georg Stahl renamed the substance phlogiston. The theory was disproved by Antoine Lavoisier in 1783, who proved the principle of conservation of mass, refuted the phlogiston theory and proposed the oxygen theory of burning.

→ phlogiston; → theory.

A speech sound considered as a physical event without regard to its place in the sound system of a language.

From Gk. phone "voice, sound," phonein "to speak;" cf. L. fama "talk, reputation, fame."

Âva "voice, sound," related to âvâz "voice, sound, song" (both prefixed forms), bâng "voice, sound, clamour" (Mid.Pers. vâng), vâžé "word," variants vâj-, vâk-, vâ-, vâz-, vât-; Av. vacah- "word," vaocanghê "to decalre" (by means of speech), from vac- "to speak, say;" cf. Skt. vakti "speaks, says," vacas- "word;" Gk. epos "word;" L. vox "voice;" PIE base *wek- "to speak."

The smallest phonetic unit in a language that can distinguish one word from another.

From Fr. phonème, from Gk. phonema "speech sound, utterance," from phonein "to sound," → phone.

Vâj "voice," variant of vâž, vâz-, âvâz etc., → phone.

A branch of linguistics dealing with the analysis, description, and classification of speech sounds. More specifically, phonetics deals with the physical production of → phonemes regardless of language, while → phonology studies how those sounds are put together to create meaningful words in a particular language.

From phonetic, from N.L. phoneticus, from Gk. phonetikos "vocal," from phonet(os) "utterable," verbal adj. of phonein "to speak clearly, utter," from → phone + -ikos, → -ics.

Âvâyik, from âvâ, → phone, + -ik, → -ics.

The branch of medical science dealing with the study and treatment of voice disorders.

From Gk. phon-, → phone; → -iatrics.

A combining form meaning "sound, voice," used in the formation of compound words. Also phon-, especially before a vowel.

From Gk. phon-, phono-, form → phone "voice, sound, speech"

A branch of linguistics that studies the rules in any given language that govern how → phonemes are combined to create meaningful words. Phonology and → phonetics study two different aspects of sound, but the concepts are dependent on each other in the creation of language.

→ phono-; → -logy.

A quantum of vibrational or acoustic energy in a crystal lattice, being the analog of a photon of electromagnetic energy.

→ phono- + → -on.

A situation in which all of the energy of a photon is transferred to an atom, molecule, or nucleus.

→ photo- + → absorption.

Th desorption of surface substances by ultraviolet radiation.

→ photo-; → desorption.

The process by which atomic nuclei are broken apart into their constituent protons and neutrons by the impact of high energy gamma photons. Photodisintegration takes place during the core collapse phase of a → Type II supernova explosion.

→ photo- + → disintegration.

The → dissociation of a → chemical compound by → radiation  → energy.

Verbal noun of → photodissociate; → -tion.

A neutral region at the boundary of a → molecular cloud created by the penetration of → far ultraviolet (FUV) radiation from associated stars. The FUV radiation (6 eV ≤ hν ≤ 13.6 eV) dissociates the molecules and heats the gas and dust. A warm, atomic → H I region is thus created and the chemistry and thermal balance of the region are determined by the penetrating FUV photons. The progressive absorption of FUV photons leads to the occurrence of transitions between atomic and molecular phases, such as H I/H₂ and C II/C I/CO transitions. By extension, any neutral region where the physics is controlled by FUV photons can be called a PDR, as it is the case for → diffuse interstellar clouds or the edge of → circumstellar disks. The PDR concept was first studied by A. G. G. M. Tielens and D. Hollenbach (1985, ApJ 291, 722).

→ photodissociation + → region.

An electron emitted from an atom or molecule by an incident photon in the → photoelectric effect.

→ photo-; + → electron.

A process going on in a molecular cloud surface whereby the surface material ionized by ultraviolet photons of neighboring stars is dissipated.

→ photo- + → evaporation.

The mechanism of raising an electron to higher energies by photon absorption, when the energy of the photon is too low to cause photoionization.

→ photo- + → excitation.

The physical process in which an incident high-energy photon ejects one or more electrons from an atom, ion, or molecule.

→ photo- + → ionization.

To cause, or to undergo → photoionization.

→ photo-; → ionize.

Subject to, or produced by → photoionization.

→ photo-; → ionized.

A calibration which converts the measured relative magnitudes into an absolute photometry.

→ photometric + → calibration.