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

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."

An evolved star whose → planetary nebula has dissipated.

→ post-; → planetary; → nebula; → star.

A short-lived transition object between the → asymptotic giant branch (AGB) and → planetary nebula phases. See also → post-asymptotic giant branch star (post-AGB).

→ pre-; → planetary; → nebula. The more commonly used term, → protoplanetary nebula, is a misnomer and must be avoided. Indeed → protoplanetary is widely used to refer to disks around → pre-main sequence stars. Since the term → protoplanet is used to denote planets undergoing formation, the use of the term "protoplanetary nebula" to mean a completely different kind of object is an unfortunate choice (Sahai et al. 2005, ApJ 620, 948).

A stage in the formation of a → planet, which comes about from the aggregation of → planetesimals. The protoplanet eventually becomes a planet by → accretion of material from a → protoplanetary disk.

→ proto- + → planet.

Of or relating to a → protoplanet or protoplanets.

→ protoplanet; → -ary.

A → circumstellar disk of gas and dust surrounding a → pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of → accretion disks which bring forth stars. Typically, their sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10⁶-10⁷ years, and accretion rates ~10^-7-10^-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of → dust grains which stick together and produce ever larger bodies, known as → planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the → snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to → Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of → giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a → debris disk around the central object that has become a → main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by → gravitational instabilities. The validity of these two theories is presently debated. See also → protoplanet.

→ protoplanet; → disk.

→ preplanetary nebula.

→ proto-; → planetary; → nebula.

A planet orbiting a → pulsar. The first such planet to be discovered was around a → millisecond pulsar known as PSR 1257+12.

→ pulsar; → planet.

The → Planck constant divided by 2π and denoted ħ, pronounced h-bar. Also called the → Dirac constant.

Reduced, p.p. of → reduce; → Planck's constant.

→ reduced Planck constant.

→ reduced Planck constant.