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

A relation between two quantities such that the first is to the second as the second is to the first. In symbols: a R b = b R a. For example, multiplication is an operation with a symmetric relation between the factors: 5 x 3 = 3 x 5.

→ symmetric; → relation.

A tensor that is → invariant under any → permutation of its indices (→ index). In other words, a tensor that equals its → transpose. For example, a second-order → covariant tensor A_jk if its components satisfy the equality: A_jk = A_kj.

→ symmetric; → tensor.

Characterized by or exhibiting → symmetry.

Adj. of → symmetry.

1) A quality of a geometric figure that has exactly similar parts with respect to a point, a line, or a plane of its own.
2) A geometric transformation that does not alter neither the shape nor the size of a figure.
3) A property of a mathematical function whose value does not change when its variables are interchanged.
4) Of physical phenomena, the property of remaining invariant under certain changes (as of rotation, reflection, inversion in space, the sign of the electric charge, parity, or the direction of time flow). See also → Noether's theorem.
See also:
→ asymmetry, → axial symmetry, → axisymmetry, → baryon asymmetry, → charge-parity symmetry, → dissymmetry, → gauge symmetry, → parity symmetry, → spherical symmetry, → spontaneous symmetry breaking, → supersymmetry, → symmetry group, → T-symmetry.

From L. symmetria, from Gk. symmetria "agreement in dimensions, due proportion, arrangement," from symmetros "having a common measure, even, proportionate," from → syn- "together" + metron "meter;" PIE base *me- "to measure;" cf. O.Pers., Av. mā- "to measure;" Skt. mati "measures;" L. metri "to measure."

Hamâmun from ham-, → syn- "together," + -â- epenthetic vowel + mun, variant mân "measure," as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," from O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure."

A group of symmetry-preserving operations composed of all rigid motions or similarity transformations of some geometric object onto itself.

→ symmetry; → group.

A prefix occurring in loanwords from Gk., having the same function as → co-; used, with the meaning "with, together," in the formation of compound words. Variants sy-, syl-, sym-, sys-.

From Gk. syn "with, together with," of unknown origin.

Ham- "together, with; same, equally, even," Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-, Skt. sam-; also O.Pers./Av. hama- "one and the same," Skt. sama-, Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-.

A line connecting the dust grains in a comet tail that left the nucleus at the same time. → syndyne.

From L. synchronus "simultaneous," from Gk. synchronos "happening at the same time," from → syn- "together" + khronos "time."

Hamzamân, from ham-, → syn- "together" + zamân, → time.

1) Going on at the same rate and exactly together. Compare → simultaneous.
2) Having the same period and phase of oscillation or cyclic movement.

From L. synchronus "simultaneous," from Gk. synchronos "happening at the same time," from → syn- "together" + khronos "time."

Hamgâm literally "at the same pace," from ham-, → syn-, + gâm "step, pace," Mid.Pers. gâm, O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes," Mod.Pers. âmadan "to come," Skt. gamati "goes," Gk. bainein "to go, walk, step," L. venire "to come," Tocharian A käm- "to come," O.H.G. queman "to come," E. come; PIE root *gwem- "to go, come."

→ synchronous rotation.

→ synchronous; → orbit.

Of a body orbiting another, where the orbiting body takes as long to rotate on its axis as it does to make one orbit. Therefore it always keeps the same hemisphere pointed at the body it is orbiting. Both bodies are tidally locked (→ tidal locking). This phenomenon is a natural consequence of → tidal braking. Synchronous rotation is common throughout the → solar system. It is found among the satellites of → Mars (→ Phobos and → Deimos), → Jupiter (most of Jupiter satellites, including the → Galilean Moons) and → Saturn (e.g. → Iapetus). Similarly, → Pluto and its moon → Charon are locked in mutual synchronous rotation, with both of them keeping the same faces towards each other.

→ synchronous; → rotation.

A type of → accelerator that accelerates charged subatomic particles (generally protons) in a circular path. Unlike → cyclotrons, in which particles follow a spiral path, synchrotrons consist of a single ring-shaped tube through which the particles loop numerous times, guided by precisely synchronized magnetic fields and accelerated at various points in the loop by electric field bursts. See also → synchrotron frequency, → synchrotron radiation.

From synchro- a combining form representing synchronized or synchronous in compound words, from L. synchronus "simultaneous," from Gk. synchronos "happening at the same time," from → syn- "together" + khronos "time" + → -tron.

Sankrotron, from Fr., as above.

The revolution frequency of a → relativistic particle of charge q and mass m in the → uniform magnetic field B of a synchrotron. It is expressed by: f_syn = qB/2πγm, where γ is the → Lorentz factor. This frequency is lower than → cyclotron frequency for a → non-relativistic case.

→ synchrotron; → frequency.

The electromagnetic radiation emitted by high-energy particles that are moving in magnetic fields, as in a synchrotron particle accelerator. The acceleration of the moving charges causes the particles to emit radiation. Radio galaxies and supernova remnants are intense sources of synchrotron radiation. Characteristics of synchrotron radiation are its high degree of polarization and nonthermal spectrum.

→ synchrotron; → radiation.

Of a comet, a curve of points calculated assuming dust grains are emitted continuously at successive instants with a constant value of the radiation pressure to gravitational attraction; also called syndyname. → synchrone.

From → syn- + dyne, → dynamics.

The working together or simultaneous action of separate elements or agencies when the result is greater than the sum of the individual effects or capabilities.

From Mod.L. synergia, from Gk. synergia "joint work, help," from synergos "working together," related to synergein "to work together, help another," from → syn- "together" + → ergon, → work, → erg.

Hamkâruži, from ham- "together," → syn-, + kâruž, → energy, + -i noun suffix.

A hypothesized rapidly spinning doughnut-shaped mass of vaporized and molten rock formed from the collision of two planet-sized objects. In numerical simulations studying giant impacts of rotating objects, a synestia can form if the total → angular momentum is greater than the → co-rotational limit. Beyond the co-rotational limit, the velocity at the equator of a body would exceed the orbital velocity (Simon J. Lock nd Sarah T. Stewart, 2017, arXiv:1705.07858v1).

From → syn- "connected; together" + Hestia the goddess of architecture.

Of or pertaining to the → conjunction of two or more heavenly bodies, especially the interval between two successive conjunctions of a planet or the Moon with the Sun.

From L.L. synodicus, from Gk. synodikos, from synodos "assembly, meeting," from → syn- "together" + hodos "a going, a way."

Hamâgam, literally "coming together," from ham-, → syn- "together," + -â- epenthetic vowel + gam from O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes," Mod.Pers. âmadan "to come," gâm "step, pace;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE stem *gwem- "to go, come."

The interval of 29.530 588 days (29d 12h 44m 2.80s), on average, between two successive → new Moons. Same as → lunation.

→ synodic; → month.

For planets, the mean interval of time between two successive → conjunctions with or → oppositions to the Sun. For example, → Mars has a synodic period of 779.9 days from Earth; thus Mars' oppositions occur once roughly 2.135 years. In comparison, the synodic period of → Venus is 583.9 days. If the sideral periods of the two bodies around the third are denoted T₁ and T₂, their synodic period is given by: 1/T_syn = |1/T₁ - 1/T₂|.

→ synodic; → period.

Grammar: A word having the same or nearly the same meaning as another in the language. Opposite of → antonym.

From L. synonymum, from Gk. synonymon "word having the same sense as another," from synonymos "having the same name as, synonymous," from → syn- "together, same" + onyma, → name.

Hamcem, from ham-, → syn-, + cem, → meaning.