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

The Serpent Holder. An extensive constellation located in the equatorial regions of the sky at about 17h 20m right ascension, 5° south declination. Although this constellation is not part of the zodiac, the Sun passes through it in December each year. Ophiuchus contains five stars of second magnitude and seven of third magnitude. Other designations: Serpent Bearer, Serpentarius. Abbreviation: Oph, genitive: Ophiuchi.

L. Ophiuchus, from Gk. ophioukhos "holding a serpent," from ophis "serpent" + echein "to hold, have, keep." The most recent interpretation is that the figure represents the great healer Asclepius, a son of the god Apollo, who learned the secrets of keeping death at bay after observing one serpent bringing another healing herbs. To prevent the entire human race from becoming immortal under Asclepius' care, Zeus killed him with a bolt of lightning, but later placed his image in the heavens to honor his good works.

Mâr-afsâ "a tamer or charmer of serpents; one who cures the snake-bitten by incantation," from mâr "snake, serpent" (Mid.Pers. mâr "snake;" Av. mairya- "snake, serpent") + afsâ agent noun of afsâyidan, from afsun "incantation" (Mid.Pers. afsôn "spell, incantation," afsûdan, afsây- "to enchant, protect by spell").

In → photometry of → binary stars or → two-body systems, the number of whole or fractional orbits completed, from the point the photometry begins. The point is conventionally chosen as the position at which the → primary star eclipses the → secondary star, and therefore the → light curve is at a minimum. The phase keeps counting indefinitely, thus the secondary star gets eclipsed at phase 0, 1, 2, 3, and so on. At these phases the primary lies between the secondary and the observer. An orbital phase of 0.5 corresponds to halfway through the binary orbit, 0.75 is three-quarters the way through, and so on.

→ orbital; → phase.

The photometric variability induced by the → orbital motion in a → two-body system.

→ orbital; → phase.

In astronautics, the study of satellite orbits and precise determination of orbital elements which gives the exact position of the satellite.

→ orbital + → -graphy.

The → number of → vertices.

→ order; → graph.

1) A child who has lost both parents through death, or, less commonly, one parent.
2) A young animal that has been deserted by or has lost its mother (Dictionary.com). → orphaned protostar.

M.E., from L.L. orphanus "destitute, without parents," from Gk. orphanos "bereaved;" akin to L. orbus "bereaved," Skt. arbhah "weak, child," Armenian orb "orphan," O.Irish orbe "heir," O.C.S. rabu "slave," Ger. Erbe, O.E. ierfa "heir," O.H.G. arabeit, Ger. Arbeit "work," O.E. earfoδ "hardship, suffering, trouble."

Yatim "fatherless," from Ar.

A → protostellar object which has been dynamically ejected from a newborn → multiple star system, either into a tenuously bound orbit or into an escape, thus depriving it from gaining much additional mass. Recent observations have shown that → Class I protostellar sources have a population of distant companions at separations ~ 1000 to 5000 → astronomical unit (AU)s. Moreover, the companion fraction diminishes as the sources evolve. According to N-body simulations of unstable → triple systems embedded in dense cloud cores, many companions are ejected into unbound orbits and quickly escape, but others are ejected with insufficient momentum to climb out of the potential well of the cloud core and associated binary. These loosely bound companions reach distances of many thousands of AU before falling back and eventually being ejected into escapes as the cloud cores gradually disappear (B. Reipurth et al. 2010, arXiv:1010.3307).

→ orphan; → protostar.

For a curve C at a point p, the limiting sphere obtained by taking the sphere that passes through p and three other points on C and then letting these three points approach p independently along C.

→ osculating; → sphere.

The condition of two oscillators that have the same frequency but different phases. Opposed to → in phase.

→ out; → phase.

The branch of physics that deals with the smallest known structures of matter and energy in order to understand the fundamental particles and forces of nature.

→ particle; → physics.

The fifteenth of Jupiter's known satellites, orbiting at 23,660,000 km from Jupiter; also known as Jupiter VIII. Its diameter is 36 km and orbital period 744 days.

In Gk. mythology, Pasiphae was the wife of Minos and mother, by a white bull, of the Minotaur.

Pertaining to, situated in, or constituting the periphery.

Adj. of → periphery.

In a charge-coupled device, the detection of charge collected by the transport register rather than by the image-sensing elements.

→ peripheral; → response.

In optics, the ability to see over large angles of view.

→ peripheral; → vision.

The external surface or boundary of a body. The circumference or perimeter of any closed figure.

From, M.E., from O.Fr. periferie, from L.L. peripheria, from Gk. peripheria "circumference, outer surface," literally "a carrying around," from peripheres "rounded, moving round," peripherein "to carry or move round," from → peri- "round about" + pherein "to carry;" cognate with Pers. bordan "to carry, lead," as below.

Pirâbar, from pirâ-, → peri-, + bar present stem of bordan "to carry, lead" (Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry;" PIE base *bher- "to carry").

A → logarithmic measure of → hydrogen ion concentration, originally defined pH = log₁₀ (1/[H⁺]), where [H⁺] is the concentration of hydrogen ions in → moles per liter of solution. The hydrogen ion concentration in pure water around room temperature is about 1.0 × 10^-7 moles. Therefore, a pH of 7 is considered "neutral," because the concentration of hydrogen ions is exactly equal to the concentration of → hydroxide (OH^-) ions produced by → dissociation of the → water. Increasing the concentration of hydrogen ions above 1.0 × 10^-7 moles produces a solution with a pH of less than 7, and the solution is considered → acidic. Decreasing the concentration below 1.0 × 10^-7 moles produces a solution with a pH above 7, and the solution is considered → alkaline or → basic. The neutral pH is different for each → solvent. For example, the concentration of hydrogen ions in pure ethanol is about 1.58 × 10^-10 moles, so ethanol is neutral at pH 9.8. A solution with a pH of 8 would be considered acidic in ethanol, but basic in water.

From Ger. PH, introduced by Danish biochemist S.P.L. Sørensen (1868-1939) in 1909, from P, for Ger. Potenz "power, potency," and H, symbol of → hydrogen.

A blue, → main sequence star of → apparent visual magnitude 2.44 and → spectral type A0 Ve located in → Ursa Major. Other designations: Phecda; Phekda; Phegda; Phekha; Phacd.

Phad, from Ar. al-Fakhidh (ad-Dubb) (الفخذ‌الدب) "the thigh (of the Bear)".

Faxez, from Ar., as above.

A hypothetical → planet which once was postulated to have existed between the orbits of → Mars and → Jupiter and its destruction supposedly led to the formation of the → asteroid belt. The idea of such a hypothetical planet was first put forward by the German astronomer Heinrich Wilhelm Olbers (1758-1840).

In Greek mythology Phaeton was the sun god Helios. Phaeton tried to drive his father's solar chariot but crashed after almost setting fire to the whole earth.

The tube or cavity, with its surrounding membrane and muscles, that connects the mouth and nasal passages with the esophagus (Dictionary.com). → throat.

From Gk pharynx (genitive pharyngos) "windpipe, throat."

Halq, loan from Ar.

1) A particular stage or point in a course, development, or graph varying cyclically; the fractional part of the period through which the time has advanced, measured from some arbitrary origin. Phase is measured like an angle, when a complete cycle is equivalent to a phase of 360° (or 2π radians), or, sometimes, as a number between 0 and 1. Two or more waves of the same frequency are → in phase when their maxima and minima take place at the same moments. Otherwise, they are said to be → out of phase or that they have a → phase difference.
2) A state in which matter can exist, depending on temperature and pressure, e.g. the → solid, → liquid, → gaseous, and → plasma states.
3) A recurring form of the → Moon or a → planet seen in the sky. → lunar phase, → phases of Venus.
4) In a → binary star system, → orbital phase.

Mod.L. phases, plural of phasis, from Gk. phasis "appearance," from stem of phainein "to show, to make appear."

1) Fâz, loanword from Fr., as above.
2) Simâ "face, aspect, resemblance."