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

Angular distance to an object measured eastward along the → ecliptic from the → vernal equinox.

→ celestial; → longitude.

Derežnâ, → longitude; âsmâni→ celestial.

A point toward which a force on a body is always directed.

→ center; → attraction.

A vast, turbulent region encircling the → Milky Way's nucleus that contains a large fraction of the → Galaxy's dense → molecular clouds and → star formation regions. Spanning -1 to +1.5 degrees of → Sgr A*, the CMZ is about 400 pc × 100 pc in size and contains at least 10⁷→ solar masses of → giant molecular clouds, approximately 10% of the Galaxy's molecular gas. The gas in the CMZ is at higher temperature than typical giant molecular clouds and has high velocity dispersion reflecting the → turbulent nature of the gas in the area. Despite these extensive molecular reserves, the → star formation rate within the CMZ is actually lower than expected based on the analysis of nearby → star-forming regions in the quiescent → Galactic disk. A common assumption is that this is a result of the extreme conditions within the CMZ, where the density, pressure, temperature, → velocity dispersion and → radiation field are all significantly greater than elsewhere in the Milky Way (Clark et al. 2018, The Messenger 173, 22 and references therein).

→ central; → molecular; → zone.

Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v²/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite.

→ centrifugal; → acceleration.

The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: a_c = v²/r = rω². According to → Newton's second law, an object undergoing centripetal acceleration is experiencing a → centripetal force.

→ centripetal; → acceleration.

A succession of → nuclear fissions when the neutrons released by previous fissions produce other nuclear fissions which themselves cause other reactions and the reactions goes on increasing exponentially.

→ chain; → reaction.

The Chameleon. A small inconspicuous → constellation in the southern hemisphere near → Crux, lying at approximate position: R.A. 11 h, Dec. -80°. Abbreviation: Cha; genitive form: Chamaeleonis;

From O.Fr. chaméléon, from L. chamaeleon, from Gk. khamaileon, from khamai "on the ground" (akin to chthon "earth;" cf. Av. zam- "the earth," Mid.Pers. zamig, Mod.Pers. zami, zamin "the earth," Skt. ksam, L. homo "earthly being" and humus "the earth," PIE *dh(e)ghom "earth") + leon "lion."

Âftâbparast "chameleon," literally "sun adorer," from âftâb "Sun, sunlight" + parast "worshipper,"

Physics: An analytical relationship between a set of physical variables that determines the state of a physical system.
Math.: The equation which is solved to find a matrix's eigenvalues, also called the characteristic polynomial.

→ characteristic; → equation.

1) The act of describing the character or qualities of someone or something.
2) The artistic representation (as in fiction or drama) of human character or motives (Merriam-Webster.com).

→ characterize; → -tion.

In particle physics, an operation that changes a particle to its antiparticle in equations describing subatomic particles or, equivalently, reverses its charge and magnetic moment.

→ charge; → conjugation.

The way a number of → electric charges are arranged in space with respect to the point of observation.

→ charge; → distribution.

A charge-transfer device that passes along stored charges positioned at predetermined locations; it is used as an image sensor in which the image points are accessed by reference to their horizontal and vertical coordinates.

→ charge; → injection; → device.

The largest satellite of Pluto. It is about 1,040 km across, roughly half Pluto's diameter. Charon is unusual in that it is the largest moon with respect to its primary planet in the Solar System. Moreover, the Pluto-Charon system is extraordinary because the center of mass lies in open space between the two, a characteristic of a double planet system. Pluto and Charon are also tidally locked in a synchronous orbit. Pluto's rotational period is 6.39 Earth days. It takes 6.39 days for Charon to make one revolution around Pluto. Thus, the two bodies continuously face each other. Also called Pluto I.

In Gk. mythology, Xαρον (Charon) was a figure who ferried the dead across the river Styx into Hades (the underworld).

Same as → chemisorption.

→ chemical; → adsorption.

A force by which chemical substances are held together by attraction of atoms to each other through sharing, as well as exchanging, of electrons.

→ chemical; → bond.

The identities, and relative abundances of the → chemical elements or → compounds that make up a substance.

→ chemical; → composition.

The symbolic representation of a chemical reaction where the formulae of the → reactants are placed on the left and the formulae of → products on the right of an arrow.

→ chemical; → equation.

A cumulative change in the chemical properties, or more specifically, the relative abundances of chemical elements in an astrophysical system.

→ chemical; → evolution.

A → change or → transformation in which a → substance → decomposes, → combines with other → substances, or interchanges constituents with other substances.

→ chemical; → reaction.

The physical processes that can cause certain elements to migrate in a → stellar atmosphere. These processes are thought to be important in creating the chemical peculiarities seen in → Am stars and → Ap stars.

→ chemical; → separation.