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

One of the phases of the Moon that appears when it is 90 degrees west of the Sun. Approximately one week after a full moon, when half of the Moon's disk is illuminated by the Sun. → first quarter.

→ last; → quarter.

Of, relating to, or like the planet → Mars.

M.E. marcien, from L. Marti(us) of, belonging to → Mars + -an a suffix of adjectives.

A piece of rock that was ejected from the Martian surface into space by the impact of an asteroid or comet, and landed on Earth. So far about 100 Martian meteorites have been collected. These meteorites have elemental and isotopic compositions that match those of the Martian crust as measured by NASA's Mars exploration missions.

→ Martian; → meteorite.

A slender, cloudy projection sometimes seen to extend from the surface of → Mars to very high altitudes. Noted and confirmed by amateur astronomers on photos of Mars in March 2012, possibly similar plumes have been found on archived images as far back as 1997. The plumes reach 200 km up, which seems too high for them to be related to wind-blown surface dust. Since one plume lasted for more than 10 days, it seemed too long lasting to be related to → aurora. The origin of this phenomenon is not yet known.

→ Martian; → plume.

A star of visual magnitude 4.8 lying 204 light-years away in the constellation → Aries. It is in fact a triple star system.

The origin of Mesarthim (or Mesartim) is a matter of controversy. Some scholars have related it to the Ar. methartim (مثرطم) "very fat (animal)," but the connection is not obvious although the words are apparently similar. The original Ar. name was Šaratayn (الشرطین) "the two marks" denoting the current β and γ stars in Aries. It was also the name of the lunar mansion of which these two stars were members. Johann Bayer (1572-1625) erroneously related Šaratayn to the Hebrew Sartai, a current term in the astrological literature of his time. Subsequently, others figured that Sartai was related to Hebrew Mesartim "servants." The Latin transliteration and alteration Mesarthim found much success in establishing itself as the proper name for star γ Arietis.

A solid particle of → nanoscale size; e.g. a → nanodust grain.

→ nano-; → particle.

An → asteroid whose orbit lies partly between 0.983 and 1.3 → astronomical units from the Sun, so that it passes close to the Earth. Currently thousands of near-Earth asteroids are known, ranging in size up to about 30 km. Among them, there are between 500 and 1,000 such asteroids larger than one km in diameter. They are divided into three subclasses: → Amor asteroids, → Apollo asteroids, and → Aten asteroids. See also → near-Earth object.

→ near; → earth; → asteroid.

An → asteroid, → comet, or large → meteoroid whose orbit brings it exceptionally close to the Earth, and which may therefore pose a collision danger. Most such objects are in orbits around the Sun with → perihelion distance less than 1.3 → astronomical units. See also → near-Earth asteroid.

→ near; → earth; → object.

An astronomical object with usually weak emission in the → visible found to be the optical representation of the object radiating chiefly in other → wavelengths of the → electromagnetic spectrum.

→ optical; → counterpart.

1) A portion or division of a whole that is separate or distinct; piece, fragment, fraction, or section; constituent.
2) A section or division of a literary work (Dictionary.com).

M.E., from O.Fr. part "share, portion; character; dominion; side, path," from L. partem (nominative pars) "a part, piece, a share, a division; a party or faction," related to portio "share, portion," from PIE root *per- "to assign, allot;" cf. Pers. pâr, pâré "piece, part, portion, fragment;" as below.

Pâr, variant pâré "piece, part, portion," parré "portion, segment (of an orange)," pargâlé, "piece, portion; patch;" (dialects Kermâni pariké "portion, half;" Tabari perik "minute quantity, particle;" Lârestâni pakva "patch;" Borujerdi parru "patch"); Mid.Pers. pârag "piece, part, portion; gift, offering, bribe;" Av. pāra- "debt," from par- "to remunerate, equalize; to condemn;" PIE *per- "to sell, hand over, distribute; to assign;" Gk. peprotai "it has been granted;" L. pars, as above; Skt. purti- "reward;" Hitt. pars-, parsiya- "to break, crumble."

Being such in part only; not total or general; incomplete.
See also: → partial derivative, → partial differential equation, → partial eclipse, → partial ionization zone, → partial lunar eclipse, → partial solar eclipse, → partial truth.

M.E. parcial, from O.Fr. parcial, from M.L. partialis "pertaining to a part," from L. pars, → part; → -al.

→ part; → -al.

The derivative of a function of two or more variables, e.g., z = f(x,y), with respect to one of the variables, the others being considered constants (denoted ∂z / ∂x).

→ partial; → derivative.

A type of differential equation involving an unknown function (or functions) of several independent variables and its (or their) partial derivatives with respect to those variables.

→ partial; → differential; → equation.

An eclipse that is not total. → partial lunar eclipse, → partial solar eclipse.

→ partial; → eclipse.

One of several zones of the stellar interior where increased → opacity can provide the → kappa mechanism to drive → pulsations. See also → Kramers' law. In these zones where the gases are partially ionized, part of the energy released during a layer's compression can be used for further ionization, rather than raising the temperature of the gas. Partial ionization zones modulate the flow of energy through the layers of the star and are the direct cause of → stellar pulsation. The partial ionization zones were first identified by the Russian astronomer Sergei A. Zhevakin (1916-2001) in the 1950s. In most stars there are two main ionization zones. The hydrogen partial ionization zone where both the ionization of neutral hydrogen (H ↔ H⁺ + e^-) and the first ionization of helium (He ↔ He⁺ + e^-) occurs in layers with a characteristic temperature of 1.5 x 10⁴ K. The second, deeper zone is called the He⁺ partial ionization zone, and involves the second ionization of helium (He⁺↔ He⁺⁺ + e^-), which occurs deeper at a characteristic temperature of 4 x 10⁴ K. The location of these ionization zones within the star determines its pulsational properties. In fact if the → effective temperature of the star is ≥ 7500 K, the pulsation is not active, because the ionization zones will be located very near to the surface. In this region the density is quite low and there is not enough mass available to drive the oscillations. This explains the blue (hot) edge of the instability strip on the → H-R diagram. Otherwise if a star's surface temperature is too low, ≤ 5500 K, the onset of efficient convection in its outer layers may dampen the oscillations. The red (cool) edge of the instability strip is believed to be the result of the damping effect of convection. He⁺ ionization is the driving agent in → Cepheids. See also → gamma mechanism.

→ partial; → ionization; → zone.

A → lunar eclipse when the Earth's → umbra passes over only part of the Moon, causing only moderate darkening of the full Moon. See also → penumbral lunar eclipse.

→ partial; → lunar; → eclipse.

A → solar eclipse when only the → penumbra of the Moon touches the Earth. The → umbra passes either just above the North Pole or just below the South Pole, missing the Earth.

→ partial; → solar; → eclipse.

A → truth value in → fuzzy logic where it can range between "completely true" and "completely false."

→ partial; → truth.

To take part, be or become actively involved.

From L. paticipatus p.p. of partcipare "to share," from particeps "partaking, sharing," from part-, pars "part," → partial, + capere "to take," → concept.

Pârgertidan, from pâr "part," → partial, + gertidan "to take," → concept.

An act or instance of participating. The fact of taking part.

Verbal noun of → participate.