An Etymological Dictionary of Astronomy and Astrophysics
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A disk of gas and dust surrounding a → protostar. These structures are rotating → accretion disks through which matter is transferred to protostars.

→ protostellar; → disk.

A high-velocity and highly → collimated jet associated with the earliest phase of → star formation that propagating along the polar axis of the → protostar-→ accretion disk system. Protostellar jets are usually detected in the [S II], [O I], and Hα lines and are therefore referred to as optical jets. They may have more than a parsec in length. Their formation is related to the → magnetohydrodynamics (MHD) of accretion disks. These jets are detected in protostellar sources over a wide range of masses, from the very early stages of formation (sources associated with infalling envelopes whose mass exceeds that of the growing star) all the way to the → classical T Tauri stars, whose envelopes have already dispersed. This phenomenon is thought to play a key role in regulating the star formation process by removing the excess → angular momentum of disk material and enabling matter to flow toward the center. Protostellar winds also provide an important → feedback mechanism between the forming star and the surrounding medium, to which they return mass and energy. Protostellar jets are at the origin of → bipolar outflows. The et sweeps up ambient → molecular cloud material into two thin shells, which manifest themselves as the observed bipolar lobes of → carbon monoxide (CO) emission. Once the molecular cloud material has been swept away (on a timescale of 10⁵ years), the bipolar outflow disappears, leaving the protostellar jet to erratically fire away for a further 10⁶-10⁷ years.

→ protostellar; → jet.

The Sun at its protostellar formation stage, before becoming a main sequence star, nearly 5 billion years ago. The protosun was more luminous than today and larger, with a radius comparable to that of the orbits of the inner planets

→ proto- + → sun.

The original or model on which something is based or formed.
Something that serves to illustrate the typical qualities of a class.

→ proto-; → type.

Capable of being demonstrated or proved.

→ prove; → -able.

To supply proof of, to establish or demonstrate the truth or validity of.

→ proof.

A short popular saying, usually of unknown and ancient origin, that expresses effectively some commonplace truth or useful thought (Dictionary.com).

→ pro-; → verb.

1) The act of provoking.
2) Something that → incites, → instigates, angers, or irritates (Dictionary.com).

Verbal noun of → provoke.

1) To anger, enrage, exasperate, or vex.
2) To stir up, arouse, or call forth (feelings, desires, or activity).
3) To → incite or → stimulate (a person, animal, etc.) to action (Dictionary.com).

M.E., from O.Fr. provoker, provochier and directly from L. provocare "call forth, challenge," from → pro- "forth" + vocare "to call," → voice.

Farâvacidan, from farâ-, → pro-, + vacidan "to call," rarr; convoke.

The forepart of a ship or boat; bow; opposite to stern or poop→ Puppis.

From M.Fr. proue, from Upper It. (Genoese) prua, from L. prora "prow," from Gk. proira, related to pro "before, forward," → pro-.

Farâl, from farâ "forward" (farâ raftan "to go forward, proceed," farâ rândan "to drive forward"), equivalent to → pro-, + relation suffix -âl, → -al. Compare farâl with prow "bow," Fr. la proue "prow, bow," from dialectal It. proa, prua, from L. prora "bow," from Gk. proira, related to pro "before, forward."

An → extrasolar planet orbiting our nearest stellar neighbor → Proxima Centauri. The planet was detected through a long-term → radial velocity campaign and found to have an → orbital period of ~ 11.2 days, a → semi-major axis of ~ 0.05 → astronomical units (20 times closer to Proxima than the Earth is to the Sun), and a minimum mass 1.3 → Earth masses (M sin i = 1.3 M_Earth), i.e. ~ 30% larger than the Earth (Anglada-Escudé et al. 2016, Nature 536, 437). The planet's surface temperature should allow it to support liquid water, and its mass suggests that it might have a rocky surface. With a semi-major axis of ~ 0.05 AU, it lies in the center of the classical habitable zone for Proxima. However, Proxima Centauri is a → flare star and the → X-ray flux received by the planet is 400 times greater than the flux that Earth receives from the Sun. Energetic particles associated with the flares may erode the atmosphere or hinder the development of primitive forms of life. It is also not known whether the → exoplanet has a magnetic field, like Earth, which could shield it from the dangerous stellar radiation.

→ Proxima Centauri.

The closest star to the Sun, lying 4.24 → light-years away. Other designations: α Centauri C, GL 551, HIP 70890, or simply Proxima. It is the faintest of the three stars that make up the → Alpha Centauri system. Proxima Centauri is a → red dwarf of → spectral type M6 Ve. It has a magnitude of +11.0, but undergoes sudden brightness increases of up to 1 mag lasting several minutes. Proxima is a late-type → flare star with a rotation period of ~ 84 days. Its mass is about 0.123 → solar masses or 129 → Jupiter masses. Proxima orbits the binary system AB at a distance of about 15,000 → astronomical unit (AU)s, with a period of approximately 550,000 years (Kervella et al., 2016, arXiv:1611.0349). In about 200,000 years it will be at the same distance as AB and in 240,000 years it will be farther to Sun than AB. It has an → effective temperature of only around 3,050 K, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. An → exoplanet, named → Proxima b, has been discovered orbiting our nearest neighbor star. Proxima experiences a seven-year activity cycle, similar to the Sun's 11-year cycle (B. J. Wargelin, B. J. et al., 2016, arXiv:1610.03447). But unlike the Sun's relatively moderate flares, Proxima's outbursts of X-ray and ultraviolet radiation could prove deadly for any hypothetical life on its planet, Proxima b.

Proxima, feminine of proximus "nearest," superlative of prope "near;" → approximate; → Centaurus.

Proksimâ, from L., as above; Kentâwros, → Centaurus; nazdiktarin, superlative of nazdik "near," from Mid.Pers. nazdik "near," from nazd "close" (Mid.Pers. nazd, nazdik "near," nazdist "first;" O.Pers. ašna- "close;" Av. nazdišta- "nearest, next," nazdyo "nearer to," nas- "to come near, approach, reach;" cf. Skt. nédīyas- "closer, very close," nas- "to approach, to reach") + -ik, → -ic.

→ Proxima b.

→ Proxima Centauri

Same as → hydrogen cyanide (HCN).

So called because it was first obtained from Prussian blue, Fe₇(CN)₁₈.

A set of astronomical tables (→ ephemeris) created in 1551 by Erasmus Reinhold (1511-1553), professor of astronomy at Wittenberg, indicating the positions of the Sun, the Moon, and the planets on the basis of the → Copernican model of heliocentric solar system. They superseded the → Alfonsine Tables, but since circular orbits were used, they were no more accurate than those tables. They were themselves replaced by the → Rudolphine Tables.

From original L. title Tabulae prutenicae "Prussian Tables," such named because Albert I, Duke of Prussia, supported Reinhold and financed the printing; → table; → zij.

A blue star, named HD 101065 or V816 Cen, with an extremely peculiar chemical composition and spectral features. Although the star has a surface temperature very close to that of stars with solar chemical composition, it displays some abundance anomalies typical of much hotter → Ap stars. The spectrum is dominated by a group of lines of → lanthanides, while in the spectra of normal stars with similar temperature the absorption lines of neutral elements from the iron group are predominant. The lanthanides may have abundances 10³-10⁴ times solar. The spectrum of Przybylski's star also shows the presence of radioactive → rare earth elements, such as → promethium and → technetium. Moreover, there are numerous strong absorption lines which defy identification. In some spectrum regions unidentified lines are more numerous than known lines. It is also a → roAp star (see, e.g., Gopka et al. 2008, Kinematics and Physics of Celestial Bodies Vol. 24, No. 2, 89).

Named after its discoverer, Antoni Przybylski (1961, Nature 189, 739).

A → retrograde irregular satellite of → Neptune discovered in 2003. Also known as Neptune X. According to preliminary estimates, it orbits Neptune at a distance of about 47 million km and takes almost 25 Earth years to make one orbit. It is about 38 kilometers in diameter.

In Gk. mythology, one of the Nereids, lover of Aeacus and mother of Phocus.

A combining form meaning "false, erroneous, pretended, unreal," used in the formation of compound words (pseudonym, pseudoclassic, pseudointellectual). In scientific use, denoting close or deceptive resemblance to the following element (pseudogene, pseudobulb, pseudocarp).
→ pseudo-disk, → pseudo-Euclidean space, → pseudo-nucleus, → pseudo-Riemannian space, → pseudoscience.

From Gk. pseudo-, combining form of pseudes "false," or pseudos "falsehood," both from pseudein "to lie, cheat, falsify."

Doruž-, from Mid.Pers. druž "false, untrue, deceptive" (Mod.Pers. doruq "lie"), drôzitan, druxtan "to lie;" O.Pers. drauga- "lie;" Av. drug- "to lie," družaiti "he lies, cheats;" cf. Skt. druhyati "he lies," drôha-, drôgha- "insult, injury," druh- "damage; ghost;" O.H.G. triogan "to deceive;" Ger. trügen "to deceive;" E. dream; PIE base *dhrugh- "to deceive, harm."

A general designation for both → box-peanut and → disk-like bulges. Although both, as opposed to the → classical bulges, show important rotational support, they also have different properties.

→ pseudo-; → bulge.

A mass structure around a → protostar that resembles an → accretion disk, but is in fact a simple flattened envelope.

→ pseudo-; → disk.