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

Same as → cross section.

→ collisional; → cross; → section.

A curve which may be represented as the intersection of a plane with a cone; hence a → parabola, → hyperbola, or → ellipse.

→ cone; → section.

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.

The act of dissecting.

→ dissect; → -tion.

The act, process, or result of intersecting.
Math.: A set of elements common to sets A and B, denoted by A ∩ B. → section.

Verbal noun of → intersect.

The minimum distance between the paths of two orbiting objects around a → primary. Such distance between an object and Earth is called Earth MOID.

→ minimum; → orbit; → intersection; → distance.

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

→ nuclear; → cross section.

A part that is cut off or separated.
A distinct part or subdivision of anything. → cross section; → intersection

From M.Fr. section, from L. sectionem "a cutting, division," from secare "to cut;" PIE base *sek- "cut" (cf. O.C.S. seko, sesti "to cut," Lith. isekti "to engrave, carve;" O.S. segasna, O.E. sigðe "scythe;" O.E. secg "sword," seax "knife, short sword").

Sekanj "a scraping, shaving, cutting," cognate with Pers. šekast-, šekastan "to break;" Av. skand- "to break," Skt. khand- "to break," khanda- "piece;" Pers. dialect Tabari šag "a special razor used to make incisions in the walls of unripe opium poppies in order to extract the milky sap," may be related to PIE *sek- "cut," as above.

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.