An Etymological Dictionary of Astronomy and Astrophysics
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An older equivalent for → asteroid.

→ planet + → -oid.

Same as → planetary science.

→ planet; + → -logy.

Variant of → plano-, as in → planisphere.

→ plane.

A projection or representation of the whole or a part of a sphere on a plane. In particular, a polar projection of the celestial sphere or the Earth on a plane.

→ plani-; → sphere.

Of or relating to → planisphere.

→ planisphere + → -ic..

The most common form of the → astrolabe in which both the → celestial sphere and the observer's horizon are projected on to one or more plane surfaces by means of the stereographic projection. See also → universal astrolabe and → particular astrolabe.

→ planispheric; → astrolabe.

The business strategy of deliberately designing products so they have a limited effective lifespan. Its objective is to incite the consumer to abandon the currently owned item and buy another one.

Planned, p.p. of "to → plan;" → obsolescence.

A combining form meaning "flat, plane," used in the formation of compound terms. Also plani- and plan- before a vowel, → plane.

→ plane.

A → divergent lens composed of one concave surface and one plane surface. This type of lens has a negative focal point and produces a → virtual image.

→ plano-; → concave; → lens.

A → convergent lens that has one flat side and one convex side. Plano-convex lenses focus parallel rays of light to a positive point, thus forming → real images.

→ plano-; → convex; → lens.

A living organism, in the Kingdom Plantae, with cellulose cell walls and lacking a nervous system or powers of voluntary motion.

M.E. plaunte; O.E. plante; L. planta "shoot, sprig, scion."

Giyâh "plant;" dialectal Bašâkardi gidâ(h), gida; Av. gaodāyu-, literally "cattle nourisher," from gao- "cattle, bull, ox," → Taurus, + dāyu- "nourisher," from dā(y)- "to feed" (Gershevitch 1962); Mod.Pers. dâyé "wet nurse;" cognate with L. femina "woman, female," → feminism; PIE base *d^heh(i)- "to suck, suckle."

A → binary system consisting of two → massive stars, which are → supergiants of → spectral types O7.5 and O6. The two components are so close together that they orbit each other with a period of 14.4 days only. The Plaskett's star is a → double-line binary. The estimated masses of the components are 43 (Plaskett A) and 51 (Plaskett B) → solar masses. The lower mass component is optically brighter than the other star. Also known as HR 2422 and HD 47129 (See, e.g., Bagnuolo et al. 1992, ApJ 385, 708).

Named after the Canadian astronomer John S. Plaskett (1865-1941), who made a detailed spectroscopic study of this star in 1922.

In physics, a gas in which an important fraction of the atoms is ionized, so that the electrons and ions are separately free. Plasma, often described as the fourth state of matter, occurs at extremely high temperatures, as in the interiors of stars, in fusion reactors, and in the interstellar medium ionized by hot stars.

From L.L. plasma, from Gk. plasma "something molded or formed," from plassein "to mold," originally "to spread thin."

Plâsmâ, loan from Fr.

In plasma physics, a dimensionless quantity which is the ratio of the plasma thermal pressure to the magnetic pressure: β = nkT/(B²/2μ₀). When β is much smaller than 1, like in the → solar corona, the magnetic forces dominate over the plasma forces.

→ plasma; β, Gk. letter of alphabet.

An alternative cosmology, initially conceived by Hannes Alfvén in the 1960s, that attempts to explain the development of the visible Universe through the interaction of electromagnetic forces on astrophysical plasma. Like the steady state model, plasma cosmology hypothesizes an evolving Universe without beginning or end.

→ plasma; → cosmology.

The natural frequency at which internal oscillations of a plasma occur. The plasma frequency is proportional to the square root of the electron density. → plasma oscillation.

→ plasma; → frequency.

(Geophysics): A layer of plasma located on the night-side of Earth, inside the magnetosphere and along its boundary. Under the action of electromagnetic forces, plasma contained in the mantle drifts equator-ward, along the tail axis.

→ plasma; → mantle.

The oscillatory motion of electrons in a neutral plasma around their equilibrium position while the ions remain at rest. When electrons are displaced by any kind of perturbation with respect to ions, a pair of positive and negative charged regions is formed. The Coulomb force accelerates back the displaced electrons, which get kinetic energy. The electrons overshoot their original positions by the same amount as their first displacement.

→ plasma; → oscillation.

The study of the physical properties of the various forms of plasmas and their processing.

→ plasma; → physics.

The ionized component of a comet's tail, driven nearly straight away from the Sun by the solar wind. Also called ion tail and gas tail.

→ plasma; → tail.