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

A suffix denoting "turned toward" that specified by the initial element; → barotropic, → isotropic, → polytropic.

From Gk. -tropos "a turn, way, manner," from tropein "to turn," from PIE base *trep- "to turn" (cf. L. trepit "he turns").

Gard "turning, changing," from gardidan "to turn, to change," Mid.Pers. vartitan, Av. varət- "to turn, revolve," Skt. vartati, L. vertere, O.H.G. werden "to become;" PIE *werto, *wer-.

Describing a medium in which certain physical properties are different in different directions.

→ anisotropy; → -ic.

A solution to Einstein's theory of → general relativity that is spatially homogeneous but allows for rotation and/or shear. See also → Bianchi cosmological model.

→ anisotropic; → homogeneous; → cosmological; → model.

In a fluid, conditions where surfaces of constant pressure are parallel to surfaces of constant temperature. This state is equivalent to zero → baroclinicity.

→ baro-; → -tropic.

A gas whose density is a function solely of pressure.

→ barotropic; → gas.

A hydrodynamical instability that arises when the horizontal → shear gradient becomes very large. Barotropic instabilities grow by extracting kinetic energy from the mean flow field.

→ barotropic; → instability.

→ Tropic of Cancer.

→ Tropic of Capricorn.

→ Capricornus.

Physical chemistry: Describing a substance that is capable of undergoing a change in phase (as from a liquid to a gas), with no change in chemical composition. If the substance is hylotropic over a limited range of pressure and temperatures, it is a pure chemical substance. If it is hylotropic over all pressure and temperatures except the most extreme ones, it is a → chemical element. See also → hylotrope.

First suggested by Wilhelm Ostwald (1904, in Annalen der Naturphilosophie 3, 355), from Gk. hylo-, combining form of hyle "matter; wood," because of the dependence on the composition, + → -tropic.

Mâdegard, from mâdé, → matter, + gard, → -tropic.

Having a constant entropy.

→ iso- + → entropy + → -ic.

A → reversible flow in which the value of → entropy remains → constant; i.e. no energy is added to the flow, and no energy losses occur due to friction or dissipative effects.

→ isentropic; → flow.

A → thermodynamic process for which there is no → heat transfer with the surroundings, and no change in → entropy.

→ isentropic; → process.

Having physical properties that do not vary with direction.

→ iso- + → -tropic.

A Universe having observed properties that appear identical in every direction.

→ isotropic; → universe.

1) Math.: Describing a function which has different values for one variable.
2) Thermodynamics: Pertaining to pressure and volume change that maintains specific heat. → polytropic process.

→ poly- + → -tropic.

A change in the → pressure or → volume of a → gas in a → polytropic process.

→ polytropic; → change.

A gas capable of undergoing a → polytropic process.

→ polytropic; → gas.

A number appearing in the equation describing a → polytropic process.

→ polytropic; → index.

A thermodynamic process that obeys the relation: PVⁿ = C, where P is pressure, V is volume, n is any real number, called the → polytropic index, and C is a constant.
If n = 0, then P = C and it is an → isobaric process.
If n = 1, then for an → ideal gas PV = NkT = C and it is an → isothermal process.
If n = γ, → adiabatic index, then for an ideal gas it is an → adiabatic process.

→ polytropic; → process.

Either of the two parallels of latitude on Earth at which the Sun appears overhead at the → summer and → winter solstices each year: → Tropic of Cancer, → Tropic of Capricorn . The tropics lie at latitudes 23°26', north and south, an angle defined by the Earth's → axial inclination.

M.E., from L. tropicus, from Gk. tropikos "of or pertaining to a turn or change; of or pertaining to to the turn of the Sun's apparent motion at solstice," from trope "a turning."

Hurgard, literally "Sun's turning," from hur, → Sun, + gard "turning, changing," from gardidan "to turn, to change;" Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend."