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

A measurement in which the comparison is directly with quantities whose units are basic units of the system. For example, the measurement of speed by measurements of distance and time is an absolute measurement, but the measurement of speed by a speedometer is not an absolute measurement. Note that the word absolute measurement implies nothing about → precision or → accuracy (IEEE Standard Dictionary of Electrical and Electronics Terms).

→ absolute; → measurement.

Same as → sound pressure.

→ acoustic; → pressure.

1) To declare earnestly to; inform or tell positively; state with confidence to.
2) To give confidence to; encourage.

M.E. as(e)uren, assuren, from O.Fr. aseurer, from L.L. assecurare, from as-, variant of → ad-, + secur-, → secure, + -a- thematic vowel, + -re infinitive suffix.

Âtenzidan, from â- intensive prefix, + tenz, → sure, + -idan infinitive suffix, → -ize.

An exposure obtained with an instrument mounted on the telescope using an artificial illuminating source in order to calibrate the instrument.

→ calibration; → exposure.

Nurdâd, → exposure; kabizeš, → calibration.

Math.: The property of a set in which the application of a given mathematical operation to any member of the set always has another member of the set as its result.
The intersection of all closed sets that contain a given set.

M.E., from M.Fr., from O.Fr. closure "that which encloses," from L. clausura "lock, fortress, a closing," from p.p. stem of claudere "to close."

Bandeš, verbal noun of bastan "to shut, bind; to clot; to form seed buds," from Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie;" Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind," cf. Ger. binden, E. bind.

A basic rule in → group theory stating that if a and b are a group element then a * b is also a group element.

→ closure; → axiom.

In astronomical interferometry, a method using triplets of telescopes in an array to calculate the phase information and get over the effects of atmospheric turbulence. The method, used in high-resolution astronomical observations, both at radio and at optical wavelengths, allows imaging of complex objects in the presence of severe aberrations.

→ closure; → phase.

The repulsive interaction due to the → Coulomb energy between two ions. If the ionic charge is Z, then the Coulomb potential energy is Z²e²/a, where a is some typical separation between the ions. The Coulomb pressure is expected to become important when the ratio Γ_C = Z²e²/akT is much larger than 1. In that case, Coulomb effects dominate those of → thermal agitation and the gas settles down into a → crystal.

→ Coulomb; → pressure.

A → CCD frame obtained with closed → shutters in the absence of any light source, in order to estimate the → dark current of the → detector.

→ dark; → exposure.

An exposure in which the detector shutter remains open for a relatively long time in order to bring out the weaker features of the observed object. In practice a deep exposure with a CCD detector is usually obtained from co-addition of shorter exposures.

→ deep; → exposure.

Pressure in a degenerate electron or neutron gas. → degenerate matter.

→ degeneracy; → pressure.

A parameter used in radio astronomy which describes the amount of dispersion in a radio signal due to its passage through an intervening plasma. It is proportional to the product of the interstellar electron density and the distance to the source.

→ dispersion; → measure.

Dissatisfaction, disapproval, or annoyance.

→ dis-; → pleasure.

A property of a moving → fluid defined by (1/2)ρv² in → Bernoulli's law, where ρ is → density of fluid and v is → velocity. Dynamic pressure is the difference between → total pressure and → static pressure. Also called → velocity pressure. → ram pressure.

→ dynamic; → pressure.

The product of the square of the electron density times the linear size of the emitting region (in parsecs).

→ emission; → measure.

1) The act of exposing; the fact or state of being exposed, → expose.
2) In optics, the total radiant energy incident on a surface per unit area. It is equal to the integral over time of the radiant flux density.

Verbal noun of → expose.

In photography, an instrument used to measure the intensity of light from a scene to be photographed and to indicate the camera lens and shutter settings required to expose the film correctly.

→ exposure; → meter.

The length of time during which the receiver is irradiated.

→ exposure; → time.

Same as → degeneracy pressure.

→ fermi; → pressure.

The term ρgz in the → Bernoulli equation. It is not pressure in a real sense, because its value depends on the reference level selected.

→ hydrostatic; → pressure.