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

The act or process of actualizing.

Verbal noun of → actualize; → -tion.

The act or process of putting into action; activation.

Verbal noun of → actuate.

The ability of the → eye to see separately two points close to each other. It is a measure of the → resolving power of the eye's → optical system and depends on the density of cells in the → retina. The maximum acuity of the normal human eye is around 0.5 minutes of arc.

→ acuity; → vision.

1) The act or process of adapting.
2) The state of being adapted.

→ adapt.

Physiological process whereby the eye adjusts its sensitivity for different levels of illumination.

→ adaptation, → eye.

Same as → adaptation.

→ adaptation.

An → adaptive optics instrument used on the → European Southern Observatory (ESO) 3.6-m telescope at La Silla. It was an upgraded version of COME-ON-PLUS, the → Very Large Telescope (VLT) adaptive optics prototype. It had 52 → actuators and performed corrections of the mirror 200 times per second. The reference → wavefront was sensed in the → visible. The observation was done in the → near-infrared (1-5 μm).

→ adaptive; → optics; → near-infrared; → system.

The operation of combining two or more quantities to obtain a third quantity called their → sum. The result of adding.

Verbal noun of → add.

The → plus sign +. It is believed to be a shortened form of the letters e and t in the L. word et, which, in early German manuscripts was the term for addition. The signs + and - were first used by Johann Wiedmann in 1489.

→ addition; → sign.

1) The act or state of adhering; state of being adhered or united.
2) Steady or devoted attachment, support, etc.; adherence.
3) Physics: The molecular force of attraction in the area of contact between unlike bodies that acts to hold them together (Dictionary.com). See also → cohesion.

Verbal noun from → adhere; → -tion.

The assumption whereby the density fluctuations in the very → early Universe would be produced by compressing or decompressing of all components of a homogeneous Universe. The adiabatic initial conditions lead to coherent oscillations in the form of peaks in the → temperature anisotropy spectrum. See also → acoustic peak, → baryon acoustic oscillation.

→ adiabatic; → initial; → condition.

The act of adopting. The state of being adopted.

→ adopt; → -tion.

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.

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."

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.

1) General: An indefinitely long period of time; an age.
2) Geology: A unit of geologic time equal to one billion years; US eon.

L. aeon, from Gk. aion "age, eternity;" akin to Av. āiiu- "duration, period, lifetime;" Skt. áyu- "life, longevity."

Âyu, from Av. āiiu- "duration, period, lifetime" (Sogd. āy "life, age"), as above.

The science and technology concerned with designing, constructing, and operating machines capable of flying in the atmosphere.

From aeronautic, from Fr. aéronautique, from aéro-, from Gk. aer, → air, + nautique "of ships," from L. nauticus, from Gk. nautikos, from naus "ship" (cognate with Mod.Pers. nâv "ship;" Av./O.Pers. *nāv-, O.Pers. nāviyā- "fleet;" Skt. nau-, nava- "ship, boat;" Gk. naus, neus, L. navis; PIE *nāu- "ship").

Havânavardi, from havâ, → air, + navardi, verbal noun of navardidan "to travel, walk, pass by and over."

The study of processes in the the upper atmosphere, especially of regions of ionized gas, from stratosphere to interplanetary space.

From Gk. aer- "weather" + nomos "arranging, regulating," related to nemein "to deal out," → -nomy.

A linear combination of vectors in which all the vector coefficients add up to one.

→ affine; → combination.