An Etymological Dictionary of Astronomy and Astrophysics
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Chemistry: The minimum amount of energy that is required to activate → atoms or → molecules to a condition in which they can undergo a → chemical reaction. Most reactions involving neutral molecules cannot take place at all until they have acquired the energy needed to stretch, bend, or otherwise distort one or more → bonds. In most cases, the activation energy is supplied by → thermal energy.

→ activation; → energy.

Energy from a source other than the conventional fossil fuel sources.

→ alternative; → energy.

Same as → rotational energy.

→ angular; → kinetic; → energy.

1) Of a gravitational system, the difference in energies between the hypothetical state where all bodies of the system are infinitely separated from each other and the actual bound state.
2) The energy which must be supplied to a nucleus in order to cause it to decompose into its constituent neutrons and protons.

Binding, noun from → bind; → energy.

Kâruž, → energy; bandeš noun from bandidan, → bind.

The quantity kT in the → Maxwell-Boltzmann distribution law, where k is → Boltzmann's constant and T the gas temperature. See also → thermal energy.

→ characteristic; → thermal; → energy

The energy associated with the chemical bonding of atoms in a solid.

→ cohesive; → energy.

The → principle whereby the → total energy of a → closed system remains → constant. This means that energy can neither be created nor destroyed. See also the → first law of thermodynamics.

→ conservation; → energy.

A principle, resulting from Einstein's theory of → special relativity whereby in any → closed system the sum of mass and energy remains → constant.

→ conservation; → mass; → energy.

Same as the → Layzer-Irvine equation.

→ cosmic; → energy; → equation.

The → potential energy from which derives the repulsive electrostatic force between two → charged particles. For example, the Coulomb energy between two protons is e²/r ~ 0.5 MeV, which is small compared with the average → binding energy per particle (~ 8 Mev). However the Coulomb repulsion becomes important for heavy nuclei. The total Coulomb energy of a nucleus is given by: (3/5) Z(Z - 1)e²/R, where Z is the → atomic number, e the charge, and R the nuclear radius. Since R ∝ A^1/3 and Z is roughly proportional to A, the Coulomb energy is roughly proportional to A^5/3. On the other hand, the total binding energy is proportional to A, which means that the relative importance of the repulsive electrostatic energy increases with increasing mass number as A^2/3.

→ coulomb; → energy.

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.

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.

Of a stellar → nuclear fusion, the equation describing the → energy generation rate as a function of → density and → temperature.

→ energy; → generation; → equation.

Of a stellar → nuclear fusion, the energy produced per unit mass per unit time, usually denoted ε (erg g^-1s^-1). The general form of the energy generation equation is: ε = ε₀ρ^λT^ν, where ε₀, ρ, and λ are constants over some efficiently restricted range of → temperature T, → density ρ, and → chemical composition. The temperature exponent ν is about 4, 15, and 40 for → proton-proton chain, → CNO cycle, and → triple alpha process, respectively.

→ energy; → generation; → rate.

Any of the several discrete states of energy which a particle, atom, or molecule can adopt under conditions where the possible values are restricted by quantum mechanical laws.

→ energy; → level.

Of cosmic rays, the plot representing the number of particles as a function of their energy.

→ energy; → spectrum.

Same as → energy level.

→ energy; → state.