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

The temperature gradient defining the → radiative equilibrium condition in a region. It is expressed as: dT/dr = (1 - 1/ γ)((T / P)(dP / dr), where T and P are temperature and pressure, dT / dr and dP / dr temperature and pressure gradients respectively, and γ = C_P / C_V. For radiative equilibrium to be stable against → convection, the actual temperature gradient must be less than the adiabatic temperature gradient, i.e. |dT /dr|_rad < |dT /dr|_ad. See also → Schwarzschild's criterion.

→ adiabatic; → temperature; → gradient.

In grammar, a word that qualifies, describes, or quantifies a noun.

M.E., from O.Fr. adjectif, from L. adjectivum "that is added to (the noun)," neuter of adjectivus "added," from p.p. of adicere "to throw or place (a thing) near," from → ad- "to" + iacere "to throw," → jet.

Zâbé, from zâb "attribute, quality" (Dehxodâ); probably related to zib "beauty, adornment," zibâ "beautiful, adorned," zivar "ornament," zab "easy; gratis; right, direct;" from Proto-Ir. *zai- "to adorn, to equip."

1) To be close to or in contact with.
2) To attach or append (dictionary.com).

M.E., from O.Fr. ajoindre"join together, unite," from L. adjungere "fasten on, harness, join to," from → ad- "to" + jungere "to bind together," cognate with → yoke.

Âbandidan, âbanidan, from prefix â- + band, vand, bastan, in dialects contracted to ban-, van- "to bind, attach," → band, + -idan infinitive suffix.

Literally "joined to." → adjoint matrix.

→ adjoin.

The → transpose of a → matrix in which each → element is replaced by its → cofactor. Same as → conjugate transpose and → Hermitian conjugate.

→ adjoint; → matrix.

1) To change (something) so that it fits, corresponds, or conforms; adapt; accommodate.
2) To put in good working order; regulate; bring to a proper state or position (Dictionary.com).

M.E. ajusten, "to correct, remedy; arrange, settle, compose," from M.Fr. adjuster, O.Fr. ajouter "to join," from L.L. adjuxtare "to bring near," from L. → ad- "to" + juxta "next," related to jungere "to join," from PIE *yeug- "to join," → conjugate, akin to E. → yoke.

Barjutidan, from prefix bar-, → on-, + Kurd. Soriani jut, jot "pair, couple, twin," Aftari jot "yoke," classical Pers. yuq, → yoke.

The act of adjusting.

Verbal noun of → adjust.

1) To choose or take as one's own; make one's own by selection or assent.
2) To take and rear (the child of other parents) as one's own child, specifically by a formal legal act.
3) To vote to accept (Dictionary.com).

M.E., from M.Fr. adopter, from L. adoptare, from → ad- + optare, → opt.

Baroptidan, on the model of bargozidan "to choose," from bar- "on, up, upon, in," → on-, + optidan, → opt.

The act of adopting. The state of being adopted.

→ adopt; → -tion.

Of or involving adoption. Acquired or related by adoption.

→ adopt; → -ive.

The second innermost known satellite of Jupiter, whose orbit is situated at a distance of about 129 000 km from the planet, and its orbital period is of 0.298 days; also known as Jupiter XV. Adrastea is 25 x 20 x 15 km in size.

In Gk. mythology, Adrastea was the daughter of Zeus and Ananke and the distributor of reward and punishments.

To take up and hold another substance on the surface.

→ adsorption.

1) A material that can hold or condense molecules of another substance on its surface by adsorption.
2) Relating to or capable of adsorption.

From → adsorb + →-ent.

Baršamandé, from baršamidan, → adsorb, + -andé.

A process in which a layer of atoms or molecules of one substance forms on the surface of a solid or liquid. → absorption, → desorption, → sorption.

Adsorption from ad- "to" + sorption, from L. sorbere "to suck," → absorption.

Baršam, from bar- "on, upon" + šam "to drink, sip," → absorption.

1) A person who is fully grown or developed or of age.
2) Having attained full size and strength; grown up; mature. A person who has attained the age of maturity as specified by law (Dictionary.com).

From L. adultus "grown up, mature, adult, ripe," p.p. of adolescere "to grow up, mature," from → ad- "to" + alescere "be nourished," from alere "to nourish."

Bornâ, from Mid.Pers. purnây- "adult;" Av. pərənāyu- "adult, old;" (Baluchi warnâ "adolescent"), literally "of full age," from pərəna-, → full, + āyu- "age," → aeon.

The slow rotation of the major axis of a planet's orbit in the same direction as the revolution of the planet itself, due mainly to gravitational interactions with other planets. The perihelion of the planet Mercury advances about 9'.6 per century. The bulk of the advance was accounted by perturbations from other planets. However, a remaining small advance, by 43'' per century, was eventually explained as an effect predicted by Einstein's theory of → general relativity. In the case of close binary stars, the advance of pericenter may additionally be caused by mass transfer and the stars' distorted (elliptical) shapes. Advance of perihelion (or pericenter) is also known as → apsidal motion.

Advance, from O.Fr. avancer "move forward," from V.L. *abantiare, from L.L. abante "from before," from ab- "from" + ante "before," PIE *ant- "front, forehead;" → perihelion.

Pišraft "advance," from piš "forward; in front; before," Mid.Pers. peš + raft "going; walk, travel," from raftan "to go."

A wave that travels backward in time according to Maxwell's electromagnetic theory; it arrives before it is transmitted. → Maxwell's equations have two solutions, the normal solution describes the ordinary waves, called → retarded waves, traveling forward in time. However, no advanced waves have ever shown up in any experiment. The advanced solutions of Maxwell's equations are usually simply discarded as "unphysical."

Advanced, adj. from advance, → advance of perihelion; → wave.

Mowj, → wave; pišras "advanced," from piš "before," Mid.Pers. peš + ras "arriving," from rasidan "to arrive," Mid.Pers. rasitan, O.Pers./Av. rasa- present stem of ar- "to move, go or come toward," cf. Skt. ar-, rcchati.

1) Geology: The process of transport of a quantity by the velocity field due to the movement of a fluid. Advection differs from → convection, which describes thermally driven circulation.
2) Meteorology: The predominantly horizontal, large-scale motions of the atmosphere. In contrast, convection describes the predominantly vertical, locally induced motions.

From L. advecti "act of conveying," from advectus, past participle of advehere "to carry," from ad-, "to" + vehere "to carry, bring;" Skt. vah-, vahati "to carry, conduct, guide," Av. vaz-, vazaiti "to guide, lead"; PIE *wegh- "to go, transport in a vehicle".

Pahnbaz from pahn "flat, wide, → broad," + baz "to carry," → evection.

The first term on the right side in the → induction equation.

→ advection; → term.

Adj. from → advection.