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

1) An act or instance of extending; the state of being extended.
2) Physics: That property of a body by which it occupies space.
3) Math.: A field F is said to be an extension of a field K if K is a subfield of F.
4) Logic: The sum of all individuals or objects to which the comprehension of a term is applied. For example, the extension of the term "dog" is the set of all (past, present and future) dogs in the world.

Verbal noun of → extend.

The discrepancy between the value of the → Hubble-Lemaitre constant inferred from a ΛCDM fit (→ Lambda cold dark matter model) to the → cosmic microwave background (CMB) and local measurements. The Universe appears to be expanding much faster now than predicted even with our latest understanding of its initial conditions and contents. Based on the → Hubble Space Telescope observations, the Hubble-Lemaitre constant is very recently estimated to be 74.03 km s^-1 Mpc^-1. This value indicates that the Universe is expanding at a rate about 9% faster than that implied by the → Planck satellite's observations of the → early Universe, which give a value for the Hubble constant of 67.4 km s^-1 Mpc^-1. For discussion, see D'Arcy Kenworthy et al. (2019, ApJ 875, 145).

→ Hubble-Lamaitre constant; → tension.

In → magnetohydrodynamic (MHD) treatment of → plasmas, that component of the → Lorentz force which is directed toward the centre of curvature of the → magnetic field lines and thus acts to straighten out the field lines. The Lorentz force can be decomposed into two components orthogonal to the magnetic field: j× B = (B . ∇) B / μ₀ - ∇ (B² / 2μ₀), where j is the → current density, μ₀ is the → magnetic permeability of free space, and B is the → magnetic flux density. The left side term is the Lorentz force, the first term on the right side is the magnetic tension and the second term the → magnetic pressure.

→ magnetic; → tension.

The inward → attraction of the → molecules at the → surface of a → liquid. The reason is that the molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. Also called surface energy and capillary forces.

→ surface; → tension.

General: The act of stretching or straining; the state of being stretched or strained.
Mechanics: The longitudinal deformation of an elastic body that results in its elongation.
Electricity: Voltage or potential; electromotive force.

M.E., from M.Fr. tension, from L. tensionem (nominative tensio) "a stretching," from tensus, p.p. of tendere "to stretch," cognate with Pers. taneš, as below.

Taneš, verbal noun from tanidan "to spin, twist, weave;" Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti "stretches," tantram "loom;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" PIE base *ten- "to stretch"), Pers. târ "string," tân "thread," tur "fishing net, net, snare," and tâl "thread" (Borujerdi dialect) belong to this family; variants tanta "cobweb," tanadu, tafen, kartané, kârtané, kâtené, Pashtu tanistah "cobweb;" cf. Skt. tantu- "cobweb, thread, string."