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

Same as → gegenschein.

A hypothetical form of energy that fills all the space and tends to increase the rate of expansion of the Universe. Assuming the existence of dark energy is a way to explain recent observations that the Universe appears to be expanding at an increasing rate (→ accelerating Universe). Dark energy seems to be a kind of anti-gravity force and is supposed to be related to → vacuum energy. Where gravity pulls things together at the more local level, dark energy tears them apart on the grander scale. The acceleration equation, one of Einstein's equations for the homogeneous Universe, indicates that if the Universe is accelerating, the pressure of the driving component should be strongly negative. The dark energy density relates to the → cosmological constant via: ρ_&Lambda = Λc²/(8πG), where G is the → gravitational constant and c the → speed of light. The first indication of dark energy was provided by the observation of → Type Ia supernovae. Other probes of dark energy are: → baryon acoustic oscillations, → weak gravitational lensing, and clusters of galaxies. In the standard model of cosmology, dark energy currently accounts for almost 74% of the total mass-energy of the Universe. Two proposed forms for dark energy are the cosmological constant and exotic component such as → quintessence.

→ dark; → energy.

Energy required to dissociate a molecule. → dissociate.

→ dissociation; → energy.

(v.intr.) To move, or extend in different directions from a common point.
Math.: Of a sequence or series, to have no unique limit.

M.L. divergere, from → di- "apart," variant of → dis- + vergere "to bend, turn, incline," from PIE *werg- "to turn," from base *wer- "to turn, bend" (cf. L. vertere "to turn," Av. varət- "to turn," Mod.Pers. gard, gardidan "to turn," Skt. vartate "turns round, rolls," Gk. rhatane "stirrer, ladle," Ger. werden, O.E. weorðan "to become."

Verâyidan, from vâ- "apart," → de-, + gerâyidan "to incline toward; to intend; to make for," infinitive of gerâ, the etymology of which is not clear. Gerâ may be a variant of Mod.Pers. kil "bent, inclined" (k/g and l/r interchanges), from PIE base *klei- "to lean, incline," cognate with L. clinare "to bend" (E. declination, inclination, etc.), Gk. klinein "to cause to slope, slant, incline," Skt. sri- "to lean," O.Pers. θray-, Av. sray- "to lean," P.Gmc. *khlinen (Ger. lehnen, E. lean).

1) The act, fact, or amount of diverging.
2) Math.: A differential → operator that, for a three-dimensional vector function F(x,y,z), is the sum of the → scalar products of the unit vectors and the partial derivatives in each of the three component directions. It is written as div F or ∇ . F = (∂F/∂x)i + (∂F/∂y)j + (∂F/∂z)k, ∇ being the → del operator or → nabla. The divergence of a vector field is a → scalar field. In physics, this operator is used to derive the amount of flux per unit volume leaving an infinitesimal element of volume at a point in a vector field. For example, in an electrostatic field, the divergence of the field is zero unless the volume element contains an electric charge.

From diverge, → diverge, + -ence a noun suffix.

Vâgerâyi, from vâgerâ stem of vâgerâyidan, → diverge, + noun suffix -i.

Same as → Gauss's theorem.

→ divergence; → theorem.

Relating to or causing divergence. Gowing away in different directions from a common point or path.
Math.: Failing to approach a limit.

M.L. divergent-, stem of divergens pr.p. of divergere, from → di- "apart," variant of → dis- + vergere "to bend, turn, incline," from PIE *werg- "to turn," from base *wer- "to turn, bend" (cf. L. vertere "to turn," Av. var ət- "to turn," Mod.Pers. gard, gardidan "to turn," Skt. vartate "turns round, rolls," Gk. rhatane "stirrer, ladle," Ger. werden, O.E. weorðan "to become."

Vâgerâ, agent noun from vâgerâyidan, → diverge + noun suffix -i.

A lens which causes a parallel beam of light passing through it to diverge or spread out; concave lens. Same as diverging lens and → negative lens.

→ divergent; → lens.

A merger between → gas-poor  → early-type galaxies.

→ dry; → merger.

1) Move out of or away from something and become visible.
2) To rise or come forth from or as if from water or other liquid (Dictionary.com).

→ ex-, + merge, → submerge.

1) The process of becoming visible after being concealed.
2) The escape of an insect or other invertebrate from an egg, cocoon, or pupal case.
3) The process of coming into existence or prominence (OxfordDictionaries.com).

→ emerge; → -ence.

1) Coming into being or notice.
2) Philo.: (of a property) arising as an effect of complex causes and not analyzable simply as the sum of their effects.
3) Ecology: Of or denoting a plant which is taller than the surrounding vegetation, especially a tall tree in a forest (OxfordDictionaries.com).

→ emerge; → -ent.

Optics: The → light ray leaving a → medium, in contrast to the → incident ray. If the medium has parallel sides, → angle of incidence and → angle of emergence

→ emergent; → ray.

A nuclear or molecular process in which some of the energy of the incoming particle is absorbed by, or transferred to, the other particle.

→ endo- + -ergic, a combining form with the meanings "activated by, sensitive to, releasing, resembling the effect produced by the substance or phenomenon specified by the initial element," from → erg, → energy + → -ic; → process.

Farâravand, → process; kâružgir, from kâruž, → energy, + gir present stem of gereftan "to take, seize, catch" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

1) Having a relatively high amount of energy.
2) Of or relating to energy.

→ energy + -t + → -ic.

Electrons and atomic nuclei ejected by solar flares, travelling with velocities amounting to a fraction of the velocity of light, and energies mostly in the range 1-100 million → electronvolts (eV), but occasionally as high as 15 billion eVs. Also known as solar → cosmic rays.

Energetic, from Gk. energetikos, from energe-, → energy, + -tikos a suffix, equivalent in meaning to → -ic, occurring in adjectives; → solar; → particle.

Zarrehâ plural of zarré, → particle; xoršidi, → solar; kâružmand from kâruž, → energy, + -mand possession suffix.

The total energy relations and transformations of energy within a particular physical, chemical, or biological system.

→ energy + -t + → -ics.

In physics, capacity for doing work.

From M.Fr. energie, from L.L. energia, from Gk. energeia "force in action, activity, operation," from energos "active, working," from en- "in, at" + ergon "work," from PIE base *werg- "to work" (cf. Av. varəz- "to work, do, perform, exercise;" Mod.Pers. varz-, varzidan "to labor, exercise, practise;" Arm. gorc "work;" Lith. verziu "tie, fasten, squeeze," vargas "need, distress;" Goth. waurkjan; O.E. wyrcan "work," wrecan "to drive, hunt, pursue").

Kâruž, literally "work strength," from kâr + už. The first component kâr "work," Mid.Pers kâr, Mod./Mid.Pers. kardan "to do, to work," Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "he makes;" cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base k^wer- "to do, to make." The second component, už, from Mid.Pers. ôž "strength" (ôžômand "strong"), Av. aogah-, aojah- "strength" (aojahvant- "strong") Skt. ojas- "strength" (ojasvant- "strong"); L. augustus "venerable," L.L. augmentare "to increase," from augere "to increase, enlarge, enrich;" Lith. augu "to grow;" Gk. auxo "increase;" Goth. aukan "to grow, increase;" O.E. eacien "to increase"); PIE *augos- "force," *aug- "to increase."

The → turbulent process whereby → kinetic energy is transformed into heat by the action of nonlinear coupling which transfers the energy from large eddies (→ eddy) to smaller and smaller eddies, finally arriving at → dissipative scales dominated by → viscosity (direct cascade). In the simplest case (3D homogeneous hydrodynamic turbulence), the resulting energy distribution is the → Kolmogorov spectrum. The reverse process also exists (inverse cascade) whereby energy is transferred to larger and larger eddies.

→ energy; → cascade.

The amount of energy in the form of radiation per unit volume, expressed in ergs cm^-3. In particular, the energy density of blackbody radiation at temperature T is aT⁴, where the radiation constant a = 7.56 × 10^-15 erg cm^-3 (K)^-4.

→ energy; → density.