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

A flat mirror with a clock-drive mounted in such a way that it moves from east to west to compensate for the apparent rotation of the Earth in order that the image of a particular area of sky remains fixed in the focal plane. See also → siderostat and → heliostat.

Coelostat, from L. coelo-, for caeli-, combination form of coelum "sky" + -stat prefix denoting something that stabilizes, keeps, fixes, from -stata, from Gk. -states "one that causes to stand," or statos "standing," from *sta- "to stand."

Âsmândâštâr, from âsmân, → sky, + dâštâr "holder, maintainer," from dâštan "to hold, maintain; to have; to possess," Mid.Pers. dâštan, O.Pers./Av. root dar- "to hold, keep back, maitain, keep in mind," Skt. dhr-, dharma- "law," Gk. thronos "elevated seat, throne," L. firmus "firm, stable," Lith. daryti "to make," PIE *dher- "to hold, support."

1) To compel by force, especially by law or authority.
2) To obtain through the use of force, threat, or other forms of constraint.

M.E., from O.Fr. cohercier, from L. coercere "to restrain, surround," form → com- "together" + arcere "to enclose, confine, keep off," from PIE *ark- "to hold, contain, guard."

Pazuridan, literally "to force against," from pa- "contrary to; against; opposing," → counter- + zur "power, force," → strength, + infinitive suffix -idan.

The act, practice, or power of using physical or moral force to compel a person to do something.

Verbal noun of → coerce.

Serving or tending to coerce.

→ coerce; → -ive.

Same as → coercive force.

→ coercive; → field.

The strength of an external → magnetic field that brings to zero the → magnetic flux density of a magnetic material when that field is caused to operate in the opposite direction from the orientation of the → magnetization of the material. Also called coercivity. Coercive force is a measure of the magnetization of a → ferromagnetic material. It is usually measured in the units of → oersted or ampere/m.

→ coercive; → force.

1) General: The quality of being coercive.
2) Physics: Same as → coercive force.

→ coercive; → -ity.

Of the same age.

From L. co-, → com-, + aevum "age," → aeon.

Hamsenn "equally old," from ham-, → com-, + senn→ age.

A number associated with an → element of a → determinant. If A is a square matrix [a_ij], the cofactor of the element a_ij is equal to (-1)^i+j times the determinant of the matrix obtained by deleting the i-th row and j-th column of A.

→ co-; → factor.

1) The mental process of knowing, including → awareness, → perception, → reasoning, and judgment.
2) The product of such a process; something thus known, perceived, etc. (Dictionary.com).

M.E. cognicioun; L. cognitionem (nominative cognitio, from cognitus p.p. of cognoscere, from → co- + gnoscere, noscere "to learn;" cognate with Pers. šenâs, šenâxt, as below.

Šenâxtâr, verbal noun of šenâxtan "to know, recognize," dânestan "to know;" O.Pers./Av. xšnā- "to know, learn, come to know, recognize;" cf. Skt. jñā- "to recognize, know," jānāti "he knows;" Gk. gignoskein "to know, think, judge;" L. gnoscere, noscere "to come to know" (Fr. connaître; Sp. conocer); O.E. cnawan; E. know; Rus. znat "to know;" PIE base *gno- "to know."

1) Of or pertaining to the act or process of knowing, perceiving, remembering, etc.; of or relating to → cognition.
2) Of or pertaining to the mental processes of perception, memory, judgment, and reasoning, as contrasted with emotional and volitional processes (Dictionary.com).

→ cognition; → -ive.

1) To stick together; be united; hold fast, as parts of the same mass.
2) Physics (of two or more similar substances) to be united within a body by the action of molecular forces (→ cohesion).

From L. cohaerere "to cleave together," from → com- "together," + haerere "to stick."

Hamdusidan, from ham- "together," → com-, + dusidan (Dehxodâ) "to stick, to adhere," → adhere.

The property of two or more electromagnetic waves when they are in fixed phase relationship over time. If the crests and troughs of the waves meet at the same time and place they are said to be in phase.

→ cohere + -ence, → -ance.

Of an → electromagnetic wave, the area of a surface perpendicular to the direction of → propagation, over which the wave maintains a specified → degree of coherence. According to the van Cittert-Zernike theorem, the coherence area is given by: A_c = D²λ²/(πd²), where d is the diameter of the light source and D is the distance away. The coherence area is an important parameter in photon correlation experiments. In the → Young's experiment the → interference pattern is only seen if slits are inside one coherence area.

→ coherence; → area.

The distance over which an → electromagnetic wave train maintains a specified → degree of coherence. The coherence length is related to the → coherence time multiplied by vacuum → velocity of light.

→ coherence; → length.

The time over which a propagating → electromagnetic wave may be considered → coherent. The coherence time of an interferometer is the interval during which the fringe phase remains stable.

→ coherence; → time.

Two or more wave sources are said to be coherent sources if the phase difference between a pair of points, one in each source, remains constant.

Coherent, adj., → coherence.

Light waves that have the same wavelength and possess a fixed phase relationship, as in a laser.

→ coherent; → light.

A branch of optics that uses coherent radiation to produce holographic three-dimensional images of objects.

→ coherent; → optics.

A scattering process in which the scattered radiation bears the same frequency and phase as the incident radiation.

→ coherent; → scattering.