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

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.

1) A broad glowing arc of radiance, sometimes seen high in the western sky at → twilight, caused by the → scattering effect of → fine dust particles suspended in the → upper atmosphere.
2) Lingering → radiation that remains after a violent → event such as a → gamma-ray burst. The afterglow of any gamma-ray burst is caused by an event different from the original explosion, likely by → shock waves colliding with the ambient medium. Afterglows occur in a large range of → electromagnetic  → wavelengths.

→ after; → glow.

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

→ alternative; → energy.

A wax-like, ash-colored, strongly scent substance present in the intestines of → whales and found in seas or cast ashore. Used in perfumery.

From M.Fr. ambre gris "gray amber," → gray; → amber.

Anbar "ambergris," from Mid.Pers. ambar.

The angle of the light coming out of a medium. For a medium with parallel sides (such as a glass slab) it is equal to the angle of incidence.

→ angle; → emergence.

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 collision of two → black holes in a → binary black hole system once they come so close that they cannot escape each other's gravity. They will merge in an extremely violent event to become one more massive black hole. The merger would produce tremendous energy and send massive ripples, called → gravitational waves, through the → space-time fabric of the Universe. Such an event (called GW150914) was first detected by the → Laser Interferometer Gravitational-Wave Observatory (LIGO) on September 14, 2015. The initial black hole masses were 36 and 29 Msun which gave a final black hole mass of 62 Msun, with 3 Msun radiated in gravitational waves. The event happened at a distance of 1.3 billion → light-years from Earth (Abbott et al., 2016, Phys. Rev. Lett. 116, 061102). Black hole merger is preceded by → inspiral and followed by → ringdown.

→ black; → hole; → merger.

An evolved star of spectral type O, B, or A; e.g. → Rigel, → Deneb.

→ blue; → supergiant.

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.

1) General: To tend to meet in a point; incline toward each other.
2) Math: (of an infinite series) to have a finite sum. (of an improper integral) to have a finite value.

From L.L. convergere "to incline together" from → com- "together" + vergere "to bend."

Hamgerâyidan, from ham- "together," → com- + gerâyidan "to incline toward, verge on; to intend," Mid.Pers. grayidan "to lean, incline; to intend, desire," → diverge.

1) General: Act or state of converging.
2) Math: The property of a → sequence or → series which ensures that it will approach a definite → finite limit. See also: → divergence.

From converg-, from → convergent + -ence, equivalent to → -ance.

Hamgerâyi, verbal noun from hamgerâyidan, → converge.

Coming together, as a light beam after passing through a convex lens which brings the beam into the focus.

Verbal ddj. from → converge.

A concave mirror that reflects a parallel beam into a convergent beam.

From → converge + → -ing; → mirror.

A highly unstable, → very massive star lying just below the empirical upper luminosity boundary in the → H-R diagram (→ Humphreys-Davidson limit) with spectral types ranging from late A to M. Cool hypergiants very likely represent a very short-lived evolutionary stage, and are distinguished by their high → mass loss rates. Many of them also show photometric and spectroscopic variability, and some have large → infrared excesses and extensive circumstellar ejecta. The evolutionary state of most of these stars is not known but they are all → post-main-sequence stars (Humphreys, 2008, IAUS 250).

→ cool; → hypergiant.

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.