An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 14 Search : nucleus
"shadow of the nucleus"
  "سایه‌ی ِ هسته"   
"sâye-ye hasté"

Fr.: "ombre du noyau"   

A dark lane that appears behind the coma in some comets. It is not the shadow of the true nucleus but sometimes may be a region of the near-tail that lies behind the densest part of the inner coma and therefore receives less sunlight.

shadow; → nucleus.

active galactic nucleus (AGN)
  هسته‌ی ِ کهکشان ِ ژیرا   
haste-ye kahkašân-e žirâ

Fr.: noyau actif de galaxie   

A central region of an → active galaxy, which is a → light-year or less in diameter and has an abnormally high luminosity. The nucleus emits high energy radiation (→ gamma rays, → X-rays, → ultraviolet) and shows → variability over various time-scales, sometimes very short (hours to weeks). Emission line spectra reveal high velocity motions up to 104 km s-1. AGNs are divided into two main types. Type I refers to an AGN whose nucleus is visible (the spectra has both narrow and broad emission lines), while in type II AGN, the broad line region (BLR) is obscured and the lines are very narrow. This may be due either to the viewing angle or some intrinsic difference in structure. See also → broad-line region, → narrow-line region, → quasar.

active; → galactic; → nucleus.

atomic nucleus
  هسته‌ی ِ اتم   
haste-ye atom (#)

Fr.: noyau atomique   

The central part of the → atom. It is made up of → protons and, in most cases, → neutrons. The nucleus is surrounded by a swarm of fast-moving → electrons. Almost all of the mass (more than 99%) of an atom is contained in the dense nucleus. The number of protons in the nucleus (called → atomic number) determines the type of → chemical element. Atoms that differ only in the number of neutrons in their nuclei are called → isotopes.

atomic; → nucleus.

comet nucleus
  هسته‌ی ِ دنباله‌دار   
haste-ye donbâledâr (#)

Fr.: noyau de comète   

The solid, centrally located part of a → comet. The nucleus is a mass of dust and frozen gases. When heated by the → Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the → coma, which is later swept into an elongated tail. Reliable measurements of cometary nuclei indicate sizes from a few km to 10 or 20 km. The nucleus of → Comet Hale-Bopp is one of the largest (perhaps 40 km). The composition of the nucleus is determined by measuring the composition of the coma (except for 67P/Churyumov-Gerasimenko). The dominant → volatile is → water, followed by → carbon dioxide (CO2), → carbon monoxide (CO), → formaldehyde (H2CO), → methanol (CH3OH), → methane (CH4) at a few percent level (with respect to water) and many other molecules at a lower level.

comet; → nucleus.

cometary nucleus
  هسته‌ی ِ دنباله‌دار   
haste-ye donbâledâr (#)

Fr.: noyau cométaire   

comet nucleus.

cometary; → nucleus.

compound nucleus
  هسته‌ی ِ همنات   
hasteh-ye hamnât

Fr.: noyau composé   

A temporary excited state of the atomic nucleus which results from the collision of an incident energetic particle with a target nucleus. Subsequently the nucleus decays by emitting particle(s).

compound; → nucleus.

condensation nucleus
  هسته‌ی ِ چگالش   
haste-ye cagâleš

Fr.: noyau de condensation   

A tiny suspended particle in the → atmosphere around which → water vapor condenses to form → droplets. Condensation nuclei are usually less than about 0.001 mm in diameter and can be made of → ice, → salt, → dust, and other materials. The droplets that form can be liquid water or ice, depending on the surrounding temperature. When the number of these droplets is large enough, a cloud is visible.

condensation; → nucleus.

false nucleus
  هسته‌ی ِ زیف   
haste-ye zif

Fr.: faux noyau   

An especially concentrated region in the → coma of some → comets, representing the dense cloud of inner coma rather than the much smaller true nucleus. Also called apparent nucleus and → pseudo-nucleus.

false; → nucleus.

galactic nucleus
  هسته‌ی ِ کهکشان   
haste-ye kahkešân

Fr.: noyau de galaxie   

A concentration of stars and gas in the innermost region of a galaxy, sometimes extending over thousands of light-years from the center of the galaxy.

galactic; → nucleus.

hasté (#)

Fr.: noyau   

1) Core of an atom, where most mass and all positive charge is concentrated. It consists of protons and neutrons.
2) Of a comet, the stellar-appearing frozen core, containing most of the cometary mass, in the head of a comet.

From L. nucleus "kernel," from nucula "little nut," diminutive of nux "nut," from PIE *knu(k) "lump" (cf. M.Ir. cnu, Welsh cneuen, M.Bret. knoen "nut," O.N. hnot, O.E. hnutu "nut").

Hasté, variants asté "kernel, fruit stone," ostoxân "bone," from Mid.Pers. astak "fruit stone, bone," ast "bone;" Av. ast- "bone;" cf. Skt. asthi- "bone;" Gk. osteon; L. os; Hittite hashtai-; PIE base *os-.

odd-even nucleus
  هسته‌ی ِ تاق-جفت   
haste-ye tâq-joft

Fr.: noyau impair-pair   

Nucleus which contains an odd number of protons and an even number of neutrons.

odd; → even; → nucleus.

odd-odd nucleus
  هسته‌ی ِ تاق-تاق   
haste-ye tâq-tâq

Fr.: noyau impair-impair   

Nucleus which contains an odd number of both protons and neutrons.

odd; → nucleus.


Fr.: pseudo-noyau   

Same → false nucleus.

pseudo-; → nucleus.

seed nucleus
  هسته‌ی ِ تخم   
haste-ye toxm

Fr.: noyau germe   

A nucleus from which a variety of → fusion  → chain reactions derive in → stellar nucleosynthesis.

seed; → nucleus.