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

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.

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

→ affine; → combination.

Any → transformation preserving → collinearity.

→ affine; → transformation.

The act of affirming or something affirmed.

Verbal noun of → affirm.

1) A jumbled cluster or mass of varied parts.
2) The act or process of agglomerating (Dictionary.com).

Verbal noun of → agglomerate.

The act or process of agitating; state of being agitated. → thermal agitation.

Verbal noun of → agitate.

Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ₀ρ)^1/2. Also called Alfvénicity.

→ Alfvénic; → fluctuation.

Large amplitude fluctuations in the → solar wind with properties resembling those of → Alfvén waves. A fluctuation is said to be Alfvénic if the following relationship between the velocity fluctuations (Δv) and magnetic field fluctuations (ΔB) is satisfied: Δv = ± ΔB/(μ₀ρ)^1/2. Also called Alfvénicity.

→ Alfvén wave; → fluctuation.

An equation in the form of P = 0, where P is a → polynomial having a finite number of terms.

→ algebra; → equation.

A function expressed in terms of → polynomials and/or roots of polynomials. In other words, any function y = f(x) which satisfies an equation of the form P₀(x)yⁿ + P₁(x)y^{n - 1} + ... + P_n(x) = 0, where P₀(x), P₁(x), ..., P_n(x) are polynomials in x.

→ algebraic + → function.

The act of allocating; the state of being allocated.

Verbal noun of → allocate.

The central and brightest of the three stars in → Orion's Belt and the fourth brightest in the whole of → Orion. Alnilam is a blue-white → supergiant of → spectral type B0 Iae with a → visual magnitude of 1.70 and a → luminosity of 375,000 times the → solar luminosity. It lies at about 1,340 → light-years.

Alnilam, from Ar. An-Nizam al-Jawza' (النظام‌الجوزاء) "the Orion's arrangement (of pearls, beads)," from nizam "arrangement" + Jawza' "Orion".

The left hand or easternmost star in → Orion's Belt, which is the fifth brightest in the whole of → Orion with a → visual magnitude of 1.79. Alnitak is a wide visual binary system consisting of components ζ Ori A (HR 1948) and ζ Ori B (HR 1949), currently separated by ~ 2''.4. ζ Ori A is a → close binary system comprising Alnitak Aa and Alnitak Ab. Aa is a hot → blue supergiant of → spectral type O9.5 Iab with an → absolute magnitude of -6.0 and an → apparent magnitude of 2.08. Its mass is estimated as being up to 33 times as massive as the Sun and to have a diameter 20 times greater. It is some 250,000 times more luminous than the Sun, with a surface temperature of about 30,000 K. It is the brightest star of class O in the night sky. Alnitak Ab is a blue → subgiant of spectral type B1 IV with an absolute magnitude of -3.9, an apparent magnitude of 4.3, and a mass of 14 Msun. Ab revolves around Ab with a period of 2,687 days. The system has a 4th magnitude companion, Alnitak B, nearly 3 arc-seconds distant. It is a B0 III type star which orbits Alnitak A every 1,500 years. Alnitak is associated with the → emission nebula  → IC 434 containing the → Horsehead Nebula.A much fainter fourth component, ζ Ori C, is located about 57'' away from ζ Ori Aa (C. A. Hummel et al., 2013, A&A 554, A52, arXiv:1306.0330).

Alnitak, from Ar. An-Nitaq al-Jawza' (النطاق‌الجوزاء) "Orion's Belt," from nitaq "belt" + Jawza "Orion."

The release of → alpha particles at high velocity from an atom's nucleus as it undergoes radioactive transformation.

→ alpha; → emission.

1) The act or process of altering; the state of being altered.
2) The result of altering.

Verbal noun of → alter.

General: Successive change from one thing or state to another and back again.
The process of periodically varying a voltage from zero to a maximum, back to zero, to a minimum, and then to zero.

Alternation, noun from → alternate.

The process by which the coating of aluminium is deposited on a telescope mirror.

Verbal noun of → aluminize.