An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) A physiological sensation received by the ear. It is caused by a vibrating source and transmitted as a longitudinal pressure wave motion through a material medium such as air.
2a) Free from damage, injury, decay, etc.
2b) Describing an → argument→ iff its → reasoning is → valid and all its → premises are → true.
2c) Logic: A formal system is sound if all the → inferences that are permitted by the rules of the system are valid inferences, that is, if no invalid arguments are provable within the system. → soundness.

1) M.E. soun; O.Fr. son, from L. sonus "sound," sonare "to sound;" PIE base *suen- "to sound;" cf. Av. x^van- "to sound;" Pers. x^vân-, x^vândan "to sing, read;" Skt. svana- "sound," svan- "to sound," svanati "it sounds;" O.E. swinn "music, song" (Cheung 2007).
2) M.E. sund, from O.E. gesund "sound, safe, having the organs and faculties complete and in perfect action," cf. O.S. gisund, O.Fris. sund, Du. gezond, O.H.G. gisunt, Ger. gesund "healthy," as in interjection gesundheit.

1) Sedâ "sound," most probably a Pers. term, since it exists also in Indo-Aryan languages: Skt. (late Vedic): sabda "articulate sound, noise," Pali and Prakriti: sadda "sound, noise," Sindhi: sadu, sado "shout, call," Gujrâti sad "call, voice, echo," Marathi: sad "shouting to," Konkani sad "sound," Sinhali: sada "sound." Therefore, sadâ in Ar. "reverberating noise, echo" maybe a loan from Pers., or a coincidence. Note that for the author of the classical Pers. dictionary Borhân-e Qâte' (India, 1652 A.D.), the Ar. term is a loanword from Pers.
2) Dorvâ (Dehxodâ) "whole, right, just;" Qâyeni, Gonâbâdi, Tabasi, Râvari dorvâx "healthy, whole," dorvâxi "health" (related to Pers. dorud "benediction, praise," dorost "whole, healthy, right"); cf. Sogd. žûk (from *druva-) "healthy;" O.Pers. duruwa- "healthy, firm, secure;" Av. druua- "healthy, firm, sound," druuatāt "health, soundness," drvô.cašman- "of sound eyes;" Skt. dhruvá- "fixed, firm;" → integral.

A sharp increase in aerodynamic drag that occurs as the speed of an aircraft approaches the speed of sound. Also called sonic barrier.

→ sound; → barrier.

The energy which → sound waves impart to a medium. Same as acoustic energy.

→ sound; → energy.

The distribution of → sound energy in a defined space.

→ sound; → field.

The maximum distance a → sound wave could have traveled through the ionized plasma from the → Big Bang until the → recombination era. It is 150 → Mpc, or bout 500 million → light-years. Sound horizon is the equivalent of the concept of → cosmic horizon, where one replaces → electromagnetic wave by → sound wave. The sound horizon is a fixed physical scale at the → last scattering surface. Cosmological models relate the value of sound horizon to the angle it subtends on the sky today. Same as acoustic horizon and sonic horizon. See also → CMB angular power spectrum.

→ sound; → horizon.

The average → sound power passing through a unit area perpendicular to the direction that the sound is traveling. It is usually expressed in watts per square meter.

→ sound; → level.

The expression of sound intensity in decibel units. The sound intensity level (L_I), in decibels, is computed as: L_I = 10 log (I/I₀), where I is the measured sound intensity and I₀ is the reference intensity (1 x 10 ^-12 watt per square meter).

→ sound; → intensity; → level.

The → sound energy emitted by a source per unit time, usually expressed in → watts. Sound power causes → sound pressure.

→ sound; → power.

The sound energy emitted by a sound source per unit time and expressed in → decibels. Sound power, in → watts, is converted to sound power level in decibels (L), by L = 10 log (W/W₀), where W₀ is the reference power (1 x 10 ^-12 watt).

→ sound; → power; → level.

The periodic fluctuation above and below atmospheric pressure created by an oscillating body which provides the → sound power. Instantaneous sound pressure is the peak value of air pressure.

→ sound; → pressure.

The number of → overtones present in a sound and their respective intensity. Like → loudness, it is a subjective quantity and cannot be measured with instruments.

→ sound; → quality.

The velocity of propagation of a → longitudinal wave in a medium under specified conditions. Also known as sonic speed, sonic velocity, acoustic velocity, sound velocity, velocity of sound, speed of sound. The speed of sound is a thermodynamic property that relates to the change in pressure and density of the medium and can be expressed as C = (dP/dρ)^1/2, where C is the sound velocity, dP is the change in pressure, and dρ the change in density. It can also be expressed as C = (E/ρ)^1/2, where E is the bulk modulus elasticity. This equation is valid for liquids, solids and gases. The sound travels faster through media with higher → elasticity and/or lower density. If a medium is → incompressible the speed of sound is infinite. For → ideal gases, a simple relationship exists between the sound speed and temperature: C = (γR T)^1/2, where γ is the → specific heat ratio (C_P/C_V), and R is the → gas constant. We see that for ideal gases it the speed is independent of pressure. In air at 0°C it is 332 m/sec. The speed of sound in a gas of hydrogen is 1315 m/s. → Mach number.

→ sound; → speed.

A → longitudinal wave which when striking the ear gives rise to the sensation of sound. Such waves can be propagated in solids, liquids, and gases. The material particles transmitting sound waves oscillate in the direction of propagation of the wave itself. There is a large range of frequencies within which longitudinal waves can stimulate the human ear and brain to the sensation of hearing. This range is from about 20 → Hz to about 20,000 Hz and is called the audible range. → ultrasound; → infrasound.

→ sound; → wave.

1) In geophysics, any penetration of the natural environment for scientific observation.
2) In meteorology, a free, unmanned balloon carrying instruments aloft to make atmospheric measurements, esp. a radiosonde balloon.
3) The measurement of the depth of water beneath a vessel.

From Fr. sonder, → sonde.

From gomâné, → sonde, + zani verbal noun of zadan "to do; to strike, beat; to play an instrument" (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill").

A small, free balloon sent into the upper atmosphere to measure, record, and transmit meteorological reports to a ground station.

→ sounding; → balloon.

1) The quality of being → sound.
2) Logic: The quality or condition of a → deductive reasoning if it meets the two conditions of → valid arguments and → true→ premises. These are the → necessary and sufficient conditions for soundness.

→ sound; → -ness.

General: Any thing or place from which something comes, arises, or is obtained.
Physics: A point, line, or area in space from which the lines of force in a vector field originate.
Electricity: Any active component, battery, or generator that supplies energy.
Thermodynamics: Any body, device, or system that provides energy.

M.E., from O.Fr. sourse "a rising, beginning, fountainhead of a river or stream," from p.p. of sourdre "to rise, spring up," from L. surgere "to rise," → surge.

Xan "source," variant xân (Gilaki xoni, Tabari xoni,Laki kyani, Tâleši xâni, xoni,); Mid.Pers. xân, xânig "source, spring," Av. xâ-, xan- "source, fountain, spring," xayana- "belonging to a spring;" cf. Khotanese khâhâ- "spring, fountain;" Skt. khâ'- "spring, source."

For a radiating material, the ratio of emissivity to opacity.

→ source; → function.

The cardinal point which is opposite to north. It is also the direction of the Sun at local noon (in the northern hemisphere).

M.E. suth(e), south(e), from O.E. suth "southward, in the south;" cf. O.S., O.Fris. suth "southward, in the south," M.Du. suut), O.H.G. sund, perhaps related to base of *sunnon "sun," with sense of "the region of the sun."

Note: South is related to right since it is to the right when one faces the rising Sun. This occurs in, for example, in Av., Skt., and O.Ir., as below.

Daštar, from Mid.Pers. dašn "right hand;" Av. dašina- "right;" Ossetic dæsni "skillful, dexterous;" cf. Skt. dáksina- "right; southern;" Gk. dexios (<*deks-i-uo-) "right," dexiteros "located on the right side;" L. dexter "right;" Goth. taihswo "right hand;" O.Ir. dess "on the right hand, southern;" PIE base *deks- "right." The second element -tar direction suffix, as in Mid.Pers. ošastar "east" (Av. ušastara- "eastern"), dôšastar "west" (Av. daôšatara-, daôšastara- "western"), abâxtar "north" (Av. apāxtara- "northern"), Mod.Pers. bâxtar, → west.

A region of the Earth where the inner → Van Allen belt comes closest to the Earth's surface. It is due to the fact that the → geomagnetic field is offset from the center of the Earth. The region is centered near 25 degrees South 50 degrees West, close to the Atlantic coast of Brazil. The excess of trapped energetic particles in that region presents a problem for satellites in orbit around the Earth.

→ south; → Atlantic; → anomaly.