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

Equal in value, measure, force, effect, significance, etc.

From L.L. æquivalentem (nominative æquivalens) "equivalent," p.p. of æquivalere "be equivalent," from L. æquus, → equal + valere "to be worth; be strong."

Hamug-arz, from hamug-, → equi-, + arz stem of arzidan "to be worth," arzân "worthy; of small value, cheap," arj "esteem, honour, price, worth;" Mid.Pers. arz "value, worth," arzidan "be worth," arzân "valuable;" Av. arəjaiti "is worth," arəja- "valuable," arəg- "to be worth;" cf. Skt. arh- "to be worth, to earn," árhant- "worthy person;" Gk. alphanein "to bring in as profit," alphein "to ear, obtain;" Lith. algà "salary, pay;" PIE base *alg^wh- "to earn; price, value."

A measure of the number of particles passing a given point in a → planetary ring per unit time. It is obtained by multiplying the physical width of the ring by its average → optical depth. For the variable-width eccentric rings of → Uranus, equivalent depth remains almost constant around a given ring (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ equivalent; → depth.

Complete set of points in any given space group which are obtained by performing the symmetry operations of the space group on a single point (x, y, z).

→ equivalent; → position.

1) A measure of the → strength of a → spectral line. The equivalent width is the width of a → rectangle centered on a spectral line that, on a plot of → intensity against → wavelength, has the same → area as the line.
2) The width-integrated → optical depth of a → planetary ring. For rings with very small optical depths, the equivalent width is very nearly equal to the equivalent depth (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ equivalent; → width.

Describing two → compound propositions → if and only if they have the same → truth table.

→ logical; → equivalent.

Same as → Joule's constant.

→ mechanical; → equivalent; → heat.

A measure of the sensitivity of an electronic detector, defined as the power input to the detector that will create a signal to noise ratio of one for an integration time of half a second.

→ noise; → equivalent; → power.

A measure of the explosive strength of a nuclear bomb, expressed in terms of the weight of → trinitrotoluene which could release the same amount of energy when exploded. The Hiroshima atomic (fission) bomb created a blast equivalent to 16 kilotons of TNT. The first hydrogen (thermonuclear) bomb test released an energy of about 10 megatons of TNT. See also → megaton of TNT.

→ trinitrotoluene (TNT); → equivalent.