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

The angular distance between the → ascending node of an object orbiting the Sun and its perihelion. Argument of perihelion is measured in the → orbital plane with respect to the Sun and in the direction of motion. It is one of the → orbital elements and usually shown with the symbol ω. See also: → argument of perigee, → argument of periapsis.

→ argument; → perihelion.

The presentation and elaboration of an argument or arguments.

Noun from → argument.

A → sequence of n numbers or quantities such that the difference between any two successive terms is a constant. In particular, if a is the first term, the nth term is a + (n - 1)d, where d is the constant. Also called → arithmetic sequence.

→ arithmetic; → progression.

An important relationship in physical chemistry that combines the concepts of → activation energy and the → Maxwell-Boltzmann distribution law. It is expressed by: k = Ae^-E_a/(RT), where k is the chemical → reaction rate, E_a is the activation energy, R is the → gas constant, and T is → temperature.

Named for Svante Arrhenius (1859-1927), Swedish chemist and physicist who suggested the relationship in 1889.

The act of ascending; ascent.

Verbal noun of → ascend; → -tion.

The act of asserting or something that is asserted.

→ assert; → -tion.

1) An appointment for a meeting.
2) The act of assigning; → assignment (Dictionary.com).

Verbal noun of → assign.

1) The act of associating, → associate; the state of being associated.
2) A group of → astronomical objects physically or apparently gathered in a particular area of sky, for example an → stellar association.
3) An organization of persons having a common interest. → dissociation.

Association, noun from → associate.

Âhazeš, verbal noun of → âhazidan→ associate. Anjoman, for the meaning 3, from Mid.Pers. anjaman, from Av. han-jamana, from han- "together" + jamana, from gam- "to come;" cf. Skt. samgamana "gathering together."

A celestial body making part of an astronomical association.

→ association; → member.

A fact or statement (as a proposition, axiom, postulate, or notion) taken for granted.

M.E., from L.L. assumption, assumptio "taking up," from L. assumere, → assume.

Âgarb, from â-, nuance prefix, + garb, from Av./O.Pers. grab-, Av. gərəb- "to take, to seize;" cf. Mod.Pers. gereftan "to take; to assume;" Skt. grah-, grabh- "to seize, to take," graha "seizing, holding, perceiving;" M.L.G. grabben "to grab;" E. grab "to take or grasp suddenly;" PIE *ghrebh- "to seize."
Ar. farz "assumption, hypothesis."

1) For an asteroid whose orbit is precisely known, a number and optionally a proper name, e.g. (7) Iris, (24101) Cassini, (99942) Apophis.
2) For an asteroid whose orbit is not known, a provisional designation composed of four elements: number.letter.letter.(optionally)number. The first number indicates the year of discovery. The first letter denotes the half-month of the discovery (A: first half of January, Y: second half of December; the letter "I" is excluded). The second letter and the following number indicate the order of discovery within the half-month. For example, the first asteroid discovered in the first half of May 1960 is: 1960 JA. Since more than 25 objects (without "I") might be detected within a half-month, the number following the second letter indicates the number of 25 discoveries. Hence, 2001 SD3 was discovered in the second half of September 2001 and was the (D =) 4 + (25 x 3) or the 79th object found during that period.

→ asteroid; → designation.

The cyclic process in which interstellar matter is incorporated into newly formed stars, where it undergoes nuclear processing, is thus enriched with heavier elements, and then returns into the interstellar medium through supernova explosion or stellar winds to be used in the formation of a newer generation of stars.

Astration, from astrate, from astr-, → astro-, + noun-forming suffix -ation.

Setâreš, from setâridan (from setâré "star" + verb-making suffix -idan) + noun-builder -eš.

The → angular → displacement of a point on the → celestial sphere due to the Earth's → atmospheric refraction.

→ astronomical; → refraction.

The absorption of → electromagnetic radiation in the → atmosphere mainly by → water vapor, → carbon dioxide, and oxygen. The atmosphere introduces two more limiting factors in → remote sensing: → atmospheric scattering and → atmospheric turbulence.

→ atmospheric; → absorption.

The large-scale movements of air around areas of high and low pressure whereby heat is distributed on the surface of the Earth. Atmospheric motion is driven by uneven heating of the planet. The atmosphere (and ocean) → transfers the excess heat from → tropics to → poles. The flow is determined by balance between → pressure gradients and the → Coriolis effect.

→ atmospheric; → circulation.

The splitting of starlight into a spectrum in the atmosphere because the atmosphere acts as a refracting prism. This phenomenon brings about a practical problem for spectroscopic observations using a slit. → differential refraction; → atmospheric refraction.

→ atmospheric; → dispersion.

The emission of electromagnetic radiation from the atmosphere due to thermal and → non-thermal processes. → Thermal emission comes mainly from → water vapor. Non-thermal processes result in emission lines oxygen (optical) and OH (near-IR). Atmospheric emission is a very significant source of noise in astronomical observations. See also → airglow, → aurora.

→ atmospheric; → emission.

The decrease in the intensity of light from a celestial body due to absorption and scattering by Earth's atmosphere. It increases from the zenith to the horizon and affects short wavelengths more than long wavelengths, so that objects near the horizon appear redder than they do at the zenith.

→ atmospheric; → extinction.

The shift in apparent direction of a celestial object caused by the bending of light while passing through the Earth's atmosphere. Since the density of the atmosphere decreases with altitude, the starlight will bend more as it continues down through the atmosphere. As a result, a star will appear higher in the sky than its true direction.

→ atmospheric; → refraction.

→ element diffusion.

→ atomic; → diffusion.