An Etymological Dictionary of Astronomy and Astrophysics

Same as → Eddington parameter.

See also: → Eddington limit; → factor.

Same as → Eddington parameter.

See also: → Eddington limit; → factor.

The theoretical upper limit of → luminosity at which the → radiation pressure of a light-emitting body would exceed the body’s → gravitational attraction. A star emitting radiation at greater than the Eddington limit would break up. The Eddington luminosity for a non-rotating star is expressed as:
L_Edd = 4πGMm_pcσ_T^-1, where G is the → gravitational constant, M the star mass, m_p the → proton mass, c the → speed of light, and σ_T the → Thomson cross section. It can also be written as L_Edd = 4πGMcκ^-1, where κ is the → opacity. In terms of solar mass, the Eddington limit can be expressed by:
L_Edd = 1.26 × 10³⁸ (M/Msun) erg s^-1. See also → rotational Eddington limit.

See also: Named after Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → limit.

The theoretical upper limit of → luminosity at which the → radiation pressure of a light-emitting body would exceed the body’s → gravitational attraction. A star emitting radiation at greater than the Eddington limit would break up. The Eddington luminosity for a non-rotating star is expressed as:
L_Edd = 4πGMm_pcσ_T^-1, where G is the → gravitational constant, M the star mass, m_p the → proton mass, c the → speed of light, and σ_T the → Thomson cross section. It can also be written as L_Edd = 4πGMcκ^-1, where κ is the → opacity. In terms of solar mass, the Eddington limit can be expressed by:
L_Edd = 1.26 × 10³⁸ (M/Msun) erg s^-1. See also → rotational Eddington limit.

See also: Named after Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → limit.

Same as → Eddington limit.

See also: → Eddington limit; → luminosity.

Same as → Eddington limit.

See also: → Eddington limit; → luminosity.

A → dimensionless parameter indicating the degree to which a star is close to the → Eddington limit. It is expressed as Γ = L / L_Edd = κ L / (4πGMc), where L and M are the star luminosity and mass respectively, κ is the opacity, c the speed of light, and G the → gravitational constant.
At the Eddington limit, Γ = 1, the star would become unbound. Because stellar luminosity generally scales with a high power of the stellar mass (L∝ M^3-4), → massive stars with M larger than 10 Msun generally have electron Eddington parameters of order Γ ≅ 0.1-1.

See also: After Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → parameter.

A → dimensionless parameter indicating the degree to which a star is close to the → Eddington limit. It is expressed as Γ = L / L_Edd = κ L / (4πGMc), where L and M are the star luminosity and mass respectively, κ is the opacity, c the speed of light, and G the → gravitational constant.
At the Eddington limit, Γ = 1, the star would become unbound. Because stellar luminosity generally scales with a high power of the stellar mass (L∝ M^3-4), → massive stars with M larger than 10 Msun generally have electron Eddington parameters of order Γ ≅ 0.1-1.

See also: After Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → parameter.

A theoretical model in which the → cosmological constant plays a crucial role by allowing an initial phase that is identical to the Einstein static Universe. After an arbitrarily long time, the Universe begins to expand. The difficulty with this model is that the initiation of galaxy formation may actually cause a collapse rather than initiate an → expansion of the Universe.

See also: → Eddington limit; Lemaître in honor of
Georges-Henri Lemaître (1894-1966), a Belgian Roman Catholic priest, who
first proposed the Big Bang theory; → universe.

A theoretical model in which the → cosmological constant plays a crucial role by allowing an initial phase that is identical to the Einstein static Universe. After an arbitrarily long time, the Universe begins to expand. The difficulty with this model is that the initiation of galaxy formation may actually cause a collapse rather than initiate an → expansion of the Universe.

See also: → Eddington limit; Lemaître in honor of
Georges-Henri Lemaître (1894-1966), a Belgian Roman Catholic priest, who
first proposed the Big Bang theory; → universe.

The time required for the redistribution of → angular momentum due to → meridional circulation. The Eddington-Sweet time for a uniformly → rotating star is expressed as:

τ_ES = τ_KH . GM / (Ω² R³), where τ_KH is the → Kelvin-Helmholtz time scale, R, M, and L designate the radius, mass, and luminosity respectively, Ω the → angular velocity, and G the → gravitational constant. The Eddington-Sweet time scale can be approximated by τ_ES≅ τ_KH / χ, where χ is the ratio of the → centrifugal force to
→ gravity. For the Sun, χ ≅ 10^-5 resulting in an Eddington-Sweet time scale which is too long (10¹² years), i.e. unimportant. In contrast, for a rotating → massive star  χ is not so much less than 1. Hence the Eddington-Sweet circulation is very important in massive stars.

See also: Named after the prominent British astrophysicist Arthur S. Eddington (1882-1944), who was the first to suggest these currents (in The Internal Constitution of the Stars, Dover Pub. Inc., New York, 1926) and P. A. Sweet who later quantified them
(1950, MNRAS 110, 548); → time scale.

The time required for the redistribution of → angular momentum due to → meridional circulation. The Eddington-Sweet time for a uniformly → rotating star is expressed as:

τ_ES = τ_KH . GM / (Ω² R³), where τ_KH is the → Kelvin-Helmholtz time scale, R, M, and L designate the radius, mass, and luminosity respectively, Ω the → angular velocity, and G the → gravitational constant. The Eddington-Sweet time scale can be approximated by τ_ES≅ τ_KH / χ, where χ is the ratio of the → centrifugal force to
→ gravity. For the Sun, χ ≅ 10^-5 resulting in an Eddington-Sweet time scale which is too long (10¹² years), i.e. unimportant. In contrast, for a rotating → massive star  χ is not so much less than 1. Hence the Eddington-Sweet circulation is very important in massive stars.

See also: Named after the prominent British astrophysicist Arthur S. Eddington (1882-1944), who was the first to suggest these currents (in The Internal Constitution of the Stars, Dover Pub. Inc., New York, 1926) and P. A. Sweet who later quantified them
(1950, MNRAS 110, 548); → time scale.

A deviation in the steady flow of a fluid causing a vortex-like motion running contrary to the general flow.
Meteo.: A small disturbance of wind in a large wind flow, which can produce turbulent conditions or turbulence.

Etymology (EN): Late M.E., from O.E. ed- “turning” + ea “water;” akin to O.N. itha.

Etymology (PE): Gižâv, from dialectical Kurd. “whirlpool,” from giž “turning,” Pers. gij “giddy-headed, vertigio;” Laki géž “whirlpool,” vagéža “whirlwind”

• âv, variant âb “water” (Mid.Pers. âb “water;” O.Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
  Hitt. happa- “water;” PIE āp-, ab- “water, river;”
  cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook”).

A deviation in the steady flow of a fluid causing a vortex-like motion running contrary to the general flow.
Meteo.: A small disturbance of wind in a large wind flow, which can produce turbulent conditions or turbulence.

Etymology (EN): Late M.E., from O.E. ed- “turning” + ea “water;” akin to O.N. itha.

Etymology (PE): Gižâv, from dialectical Kurd. “whirlpool,” from giž “turning,” Pers. gij “giddy-headed, vertigio;” Laki géž “whirlpool,” vagéža “whirlwind”

• âv, variant âb “water” (Mid.Pers. âb “water;” O.Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
  Hitt. happa- “water;” PIE āp-, ab- “water, river;”
  cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook”).

An induced current circulating in masses of metal moving in a magnetic field or located in a changing magnetic field. Also known as → Foucault current.

See also: → eddy; → current.

An induced current circulating in masses of metal moving in a magnetic field or located in a changing magnetic field. Also known as → Foucault current.

See also: → eddy; → current.

A macroscopic process that occurs in a → fluid because of the relative motions induced by the non-uniform → turbulent motions of the fluid.
Also known as turbulent → diffusion. Eddy diffusion may occur in an atmosphere if it is unstable against turbulence. It dominates the atmosphere below the homopause. See also → molecular diffusion.

See also: → eddy; → diffusion.

A macroscopic process that occurs in a → fluid because of the relative motions induced by the non-uniform → turbulent motions of the fluid.
Also known as turbulent → diffusion. Eddy diffusion may occur in an atmosphere if it is unstable against turbulence. It dominates the atmosphere below the homopause. See also → molecular diffusion.

See also: → eddy; → diffusion.

1. A line or border at which a surface terminates.
   

2. The thin, sharp side of the blade of a cutting instrument or weapon (Dictionary.com).
   

3. In → graph theory, any line in a → graph that joins two distinct → nodes. Any pair of → vertices.

Etymology (EN): M.E. egge; O.E. ecg “corner, edge;” cf.
Ger. Eck “corner;” PIE base *ak- “sharp, pointed” (cf. L. acies; Gk. akis “point”).

Etymology (PE): 1) Labé “limb, edge,” from lab “lip;” Mid.Pers. lap; cognate with L. labium; E. lip; Ger. Lefze.

2. Tiqé “blade of a knife or sword,” from tiq “blade,” tiz “sharp,” variants tig, tež, tej, tij; Mid.Pers. tigr, têz, têž “sharp,” O.Pers. tigra- “pointed,”
   tigra.xauda- “pointed helmet (epithet of Scythians);” Av. tiγra- “pointed,” tiγray- “arrow,” tiži.arštay- “with the pointed spear,” cf. Skt. tikta- “sharp, pungent, bitter,” tejas- “sharpness, edge, point or top of a flame;” PIE base *st(e)ig- “to stick; pointed.” Cognates in other IE languages: Gk. stizein “to prick, puncture,” stigma “mark made by a pointed instrument,” L. in-stigare “to goad,” O.H.G. stehhan, Ger. stechen “to stab, prick,” Du. stecken, O.E. sticca “rod, twig, spoon,” E. stick.

1. A line or border at which a surface terminates.
   

2. The thin, sharp side of the blade of a cutting instrument or weapon (Dictionary.com).
   

3. In → graph theory, any line in a → graph that joins two distinct → nodes. Any pair of → vertices.

Etymology (EN): M.E. egge; O.E. ecg “corner, edge;” cf.
Ger. Eck “corner;” PIE base *ak- “sharp, pointed” (cf. L. acies; Gk. akis “point”).

Etymology (PE): 1) Labé “limb, edge,” from lab “lip;” Mid.Pers. lap; cognate with L. labium; E. lip; Ger. Lefze.

2. Tiqé “blade of a knife or sword,” from tiq “blade,” tiz “sharp,” variants tig, tež, tej, tij; Mid.Pers. tigr, têz, têž “sharp,” O.Pers. tigra- “pointed,”
   tigra.xauda- “pointed helmet (epithet of Scythians);” Av. tiγra- “pointed,” tiγray- “arrow,” tiži.arštay- “with the pointed spear,” cf. Skt. tikta- “sharp, pungent, bitter,” tejas- “sharpness, edge, point or top of a flame;” PIE base *st(e)ig- “to stick; pointed.” Cognates in other IE languages: Gk. stizein “to prick, puncture,” stigma “mark made by a pointed instrument,” L. in-stigare “to goad,” O.H.G. stehhan, Ger. stechen “to stab, prick,” Du. stecken, O.E. sticca “rod, twig, spoon,” E. stick.

A → spiral galaxy oriented edge-on to our view. → face-on galaxy.

Etymology (EN): → edge; on, from O.E. on, variant of an “in, on, into”
(cf. Du. aan; Ger. an; Goth. ana “on, upon”), from PIE base *ano “on” (cf. Av. ana “on;” Gk. ana “on, upon;” L. an-); → galaxy.

Etymology (PE): Kahkašân, → galaxy; pahlunemâ “showing the side,” from pahlu, → side, + nemâ, from nemudan “to show, display,” → display.

A → spiral galaxy oriented edge-on to our view. → face-on galaxy.

Etymology (EN): → edge; on, from O.E. on, variant of an “in, on, into”
(cf. Du. aan; Ger. an; Goth. ana “on, upon”), from PIE base *ano “on” (cf. Av. ana “on;” Gk. ana “on, upon;” L. an-); → galaxy.

Etymology (PE): Kahkašân, → galaxy; pahlunemâ “showing the side,” from pahlu, → side, + nemâ, from nemudan “to show, display,” → display.

To modify or prepare for publication or public presentation by checking,
improving, cutting, rearranging, etc.

Etymology (EN): Back formation from editor or from Fr. éditer, or from L. editus, p.p. of edere “bring forth, produce,” from → ex- “out,” + -dere, combining form of dare “to give,” → datum.

Etymology (PE): Virâstan, from Mid.Pers. virâstan “to arrange, prepare, restore,”
from prefix vi- “apart, away from, out” (Av. vi-; O.Pers. viy- “apart, away;” cf. Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + râstan “to arrange, to set in order,” → coordinate.

To modify or prepare for publication or public presentation by checking,
improving, cutting, rearranging, etc.

Etymology (EN): Back formation from editor or from Fr. éditer, or from L. editus, p.p. of edere “bring forth, produce,” from → ex- “out,” + -dere, combining form of dare “to give,” → datum.

Etymology (PE): Virâstan, from Mid.Pers. virâstan “to arrange, prepare, restore,”
from prefix vi- “apart, away from, out” (Av. vi-; O.Pers. viy- “apart, away;” cf. Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + râstan “to arrange, to set in order,” → coordinate.

1. The act or process of editing.
   

2. A version of anything, printed or not, presented to the public.

See also: Verbal noun of → edit.

1. The act or process of editing.
   

2. A version of anything, printed or not, presented to the public.

See also: Verbal noun of → edit.

1. A person who edits material for publication or public presentation.
   

2. A computer program that enables creating and editing text files.

See also: Agent noun of → edit.

1. A person who edits material for publication or public presentation.
   

2. A computer program that enables creating and editing text files.

See also: Agent noun of → edit.

1. An article in a newspaper or other periodical or on a website presenting the opinion of the publisher, writer, or editor.
   

2. A statement broadcast on radio or television that presents the opinion of the owner, manager, or the like, of the program, station, or channel (Dictionary.com).

See also: → editor + -i- + → -al.

1. An article in a newspaper or other periodical or on a website presenting the opinion of the publisher, writer, or editor.
   

2. A statement broadcast on radio or television that presents the opinion of the owner, manager, or the like, of the program, station, or channel (Dictionary.com).

See also: → editor + -i- + → -al.

To give knowledge or develop the faculties and powers of somebody by teaching. instruction.

Etymology (EN): From L. educatus, p.p. of educare “bring up, rear, educate,” from → ex- “out” + ducere “to lead.”

Etymology (PE): Farhixtan, “educate,” literally “drawing forward, pulling up;” from far- perfection prefix, → pro-, + hanjidan “to draw,” → culture.

To give knowledge or develop the faculties and powers of somebody by teaching. instruction.

Etymology (EN): From L. educatus, p.p. of educare “bring up, rear, educate,” from → ex- “out” + ducere “to lead.”

Etymology (PE): Farhixtan, “educate,” literally “drawing forward, pulling up;” from far- perfection prefix, → pro-, + hanjidan “to draw,” → culture.

The act or process of educating.
The knowledge or abilities gained through being educated.

See also: Verbal noun of → educate.

The act or process of educating.
The knowledge or abilities gained through being educated.

See also: Verbal noun of → educate.