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

In an imaging system, the unvarying of the → point spread function over an extended field of view.

From isoplanat(ic), → isoplanatic, + → -ism.

The condition in which the wavefronts arriving from different parts of a region of sky undergo almost identical phase perturbations. See also → isoplanatic patch.

→ isoplanatic; → patch.

An airplane moved by → jet propulsion.

→ jet; plane, short for airplane, from Fr. aeroplane, from aero-, → air, + plane feminine of plan "flat, level," from L. planus, perhaps by association with forme plane; apparently coined and first used by Fr. sculptor and inventor Joseph Pline in 1855.

→ jet; havâpeymâ "airplane," from havâ, → air, + peymâ "travelling; traveller," from peymudan, peymâyidan "to travel, traverse, pass over," from Mid.Pers. patmudan, paymudan "to measure (against)," from *pati-māya-. The first element *pati- "against, back" (cf. Mod.Pers. pâd- "against, contrary to;" Mid.Pers. pât-; O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti; Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti). The second element from *mā- "to measure;" O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure." Apart from peymâ, several other terms in Mod.Pers. are related to this second element, which occurs also as mun, mân, man, mâ, mu, and mây: pirâmun "perimeter," âzmun, âzmây- "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," man "a measure weighing forty seers)," nemudan, nemâ- "to show, display," âmâdan, âmây- "to prepare."

A planet that does not have a well-defined → solid  → crust, such as any of the four Solar System outer, gaseous planets: → Jupiter, → Saturn, → Uranus, and → Neptune.

→ Jovian; → planet.

The plane normal to the axis about which the pole of a satellite's orbit → precesses. In his study of Jupiter's satellites, Laplace (1805) recognized that the combined effects of the solar tide and the planet's oblateness induced a "proper" inclination in satellite orbits with respect to Jupiter's equator. He remarked that this proper inclination increases with the distance to the planet, and defined an orbital plane (currently called Laplace plane) for circular orbits that lies between the orbital plane of the planet's motion around the Sun and its equator plane (Tremaine et al., 2009, AJ, 137, 3706).

→ Laplace; → plane.

A name used to describe any planet that is considerably larger and more massive than the Earth, and contains large quantities of hydrogen and helium. Jupiter and Neptune are examples of major planets.

→ major; → planète.

An obsolete name used to describe an → asteroid.

→ minor; → planet.

A stellar system with more than one orbiting planet.

→ multi-; → planet; → system.

A hypothetical → exoplanet covered by a water envelope. The presence of such a planet stems from the implicit assumption of → Habitable Zone temperatures and a liquid water surface.

→ ocean; → planet.

The plane defined by the motion of an object about a primary body.

→ orbital; → plane .

For a curve C at a point p, the limiting plane obtained from taking planes through the tangent to C at p and containing some variable point p' and then letting p' approach p along C.

→ osculating; → plane.

A planet that revolves around the Sun beyond the → asteroid belt, namely → Jupiter, → Saturn, → Uranus, and → Neptune.

→ out; → planet.

1a) A scheme or method of acting, doing, proceeding, making, etc., developed in advance.
1b) A representation of a thing drawn on a plane, as a map or diagram.
2a) To arrange a method or scheme beforehand for.
2b) To make plans for (Dictionary.com).

M.E., from Fr. plan "ground plan, map," literally "plane surface," from L. planum "level or flat surface," noun use of adjective planus "level, flat" (from PIE root *pele- "flat; to spread;" Gk. plassein "to mold," plasma "something molded or created;" L. planus "flat, level, even, plain, clear;" Lith. plonas "thin;" O.C.S. polje "flat land, field," Russ. polyi "open;" O.E. feld, M.Du. veld "field."

Pišgâr, literally "beforehand written, painted in advance," from piš- "before, in front," → pre-, + gâr present stem of negâridan, negâštan "to paint, write," → graph.

Variant of → plano-.

→ plano-.

Short for Max Planck (1858-1947), German physicist, great authority on thermodynamics and creator of the quantum theory.

A physical constant that determines the energy of quantum as a function of its frequency; symbol h. Also called → Planck's constant. On 16 November 2018, the International Bureau of Weights and Measures (BIPM) voted to redefine the kilogram by fixing the value of the Planck constant, thereby defining the kilogram in terms of the second and the speed of light. Starting 20 May 2019, the new value is exactly 6.626 070 15 × 10^-34 J s. The → reduced Planck constant, ħ = h / 2π, is also called the → Dirac constant.

→ Planck; → constant.

Same as → blackbody curve.

→ Planck; → curve.

The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρ_P = c⁵/(ħG²) ≅ 5.16 x 10⁹³ g cm^-3, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant.

→ Planck; → density.

The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law.

→ Planck; → distribution.

The unit of energy in the system of Planck units. E_P = √ (ħ c⁵/G) ≅ 1.22 x 10¹⁹ GeV. It can also be defined as E_P = ħ / t_P, where t_P is the Planck time. This is an extraordinarily large amount of energy on the subatomic scale and particle accelerators have yet to produce a particle with this magnitude of energy. Understanding the properties of a subatomic particle that contains the Planck Energy is helpful in developing a Unified Field Theory which encompasses the realms of Quantum Theory and Relativity, although this too has evaded complete scientific understanding.

→ Planck; → energy.