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

Same as → cross section.

→ collisional; → cross; → section.

1a) The Southern Cross, → Crux. 1b) A figure or pattern formed by the intersection of two lines.
2a) (adj.) Involving interchange; reciprocal.
2b) Lying or passing crosswise; intersecting.
3) To move or go across (something); traverse or intersect.

M.E. cros, from O.E., probably from Old Norse kross, from O.Ir. cros, from L. crux "stake, cross."

Calipâ, loanword from Aramaic.
Xâj loanword from Arm.
Gozaštan, Mid.Pers. vitartan "to pass," Sogdian wytr "to go," O.Pers./Av. vitar- "to put across," from prefix vi- "away, apart," + tar- "to cross over" (Skt. tr- "to cross over," tarati "crosses," cf. Av. taro, Skt. tirah "through, beyond," L. trans "beyond," Ger. durch, E. through; PIE base *tr- "through").

In radio astronomy, the process performed by a → cross correlator or the result of the process.

→ cross; → correlation.

In radio interferometry, a device that multiplies together the signals received by each pair of antennas in an array and performs several operations on the signal (filtering out the noise added to the signal by the receiver electronics, correcting for the Doppler shift and geometric delay due to the position and motion of the antennas). The correlated signal, corresponding to the spatial frequency given by the distance between the two antennas, is then combined with the other spatial frequency to reconstruct the map of the source.

→ cross; → correlator.

A device producing cross dispersion.

→ cross; → disperser.

Dispersion of a light beam by using two dispersing elements (grating, grism), one for separating spectral orders, the other for resolving spectral features within an order.

→ cross; → dispersion.

The identification of an object in a data base or catalog and matching it with the same object identified in another catalog.

→ cross; → identification.

Same as → vector product.

→ cross; → product.

Reference from one part or element of a book or data catalog to something in another for further information.

→ cross; → reference.

1) Math: The intersection of a plane with a geometric figure, usually at right angles to an axis of symmetry.
2) Physics: A quantity that expresses the effective area that a given particle presents as a target to another incident particle, giving a measure of the probability that the incident particle will induce a particular atomic or nuclear reaction. Also called collision cross section. The cross section has the dimensions of a surface. In nuclear and particle physics, the commonly used units for the cross section are the barn and cm².

In classical mechanics, the cross section for the collision of a point particle with a hard sphere is just be the surface of a section through the middle of the sphere. This explains the name "cross section." → cross; → section.

A spectrograph that utilizes cross dispersion.

→ cross; → dispersion; → spectrograph.

A system of two perpendicular fine threads of wire placed in the focus of the eyepiece of an optical instrument and used as a sighting reference.

→ cross; → hair.

Târbast, from târ + bast. The first component târ "thread, string, wire," cognate with tanidan, tan- "to spin, twist, weave," → tension; the second component bast "to bind; to arrange" (past stem of bastan, from Mid.Pers. bastan/vastan "to bind, shut," → band.

A concept used for checking the stability of a group of mass such as a → cluster of galaxies or a → star cluster. The crossing time is given by t_c = R/V, where R is the average projected radial distance of group members from the center of mass and V the Gaussian dispersion in internal velocity.

→ cross; → time.

An image of a distant quasar (redshift 1.7) formed by a foreground spiral galaxy (redshift 0.039) through gravitational lensing. The image of the quasar is split into four point sources forming a cross at the center of the galaxy.

→ Einstein; → cross.

A → radiationless relaxation process in which a molecule in some excited → electronic state converts to a state of different spin → multiplicity. Intersystem crossing is analogous to → internal conversion.

→ intersystem; → crossing.

A design of → radio interferometer made of two lines of → antennae at right angles to one another.

Named after the Australian engineer and astronomer Bernard Yarnton Mills (1920-2011; see R.H. Frater et al. 2013, arXiv:1306.6371); → cross.

An arrangement of stars in the form of a cross in the constellation → Cygnus.

→ north; → cross.

Apparent cross-section possessed by an atomic nucleus when it undergoes a particular type of collision process.

→ nuclear; → cross section.

Popular name for the constellation → Crux. Its four brightest stars form a distinctive cross shape.

→ southern; → Crux.

The → cross section involved the → Thomson scattering of electromagnetic waves by a free electron. It is defined by: σ_T = 8πr_e²/3, where r_e is the classical → electron radius. Its value is 0.665 245 x 10^-28 m².

→ Thomson; → cross; → section.