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

An → electric current that reverses direction of flow at regular intervals. The typical alternating current is → sinusoidal in shape. Alternating current has the advantage over → direct current in that its → voltage magnitude can be changed easily through a → transformer. Moreover, it is safer to transfer over the longer city distances and can provide more → power. The frequency of alternating current is 50 Hz (Europe) or 60 Hz (USA).

→ alternating; → current.

1) Existing, happening, or done at the same time.
2) Acting in conjunction; cooperating. → concurrent forces.

Verbal adj. from → concur.

A system of forces applied to a → rigid body in such manner that their lines of action intersect at a single point. A system of concurrent forces acting on a rigid body can be replaced by an equivalent force applied at the same point. → line of action.

→ concurrent; → force.

Any steady movement of material in space. In particular, any movement of electric charge. → stream; → flow; → flux.

From O.Fr. corant "running," pr.p. of courre "to run," from L. currere "to run," from PIE *kers- "to run" (cf. Gk. -khouros "running," Lith. karsiu "go quickly," O.N. horskr "swift," Welsh carrog "torrent").

Jarayân from Ar.

The → Universe at the → redshift z = 0.

→ current; → cosmological; → epoch.

The electric current per unit of cross-sectional area perpendicular to the direction of current flow. It is a vector quantity and represented by symbol J. Electric current density is usually expressed in amperes per square meter.

→ current; → density

Current generated in an electronic detector by thermal effects, even in the absence of input signal. In a → CCD detector, the current rises from thermal energy within the silicon lattice comprising the CCD. These electrons are captured by the CCD's potential wells and counted as signal. → dark current noise.

→ dark; → current.

In a → CCD detector, statistical fluctuation of the → dark current, equal to the square root of the dark current. CCDs can be cooled either with thermoelectric coolers or liquid nitrogen to reduce this effect. Ideally, the dark current noise should be reduced to a point where its contribution is negligible over a typical exposure time.

→ dark; → current; → noise.

An → electric current which flows in one direction only and which is substantially constant in magnitude. Virtually all electronic and computer hardware needs direct current to function. → Alternating current can be converted to direct current by means of a power supply consisting of a → transformer.

→ direct; → current.

In electromagnetism, a quantity which is not a real current (movement of charge), but has the units of current and has an associated magnetic field. The physical meaning of this displacement current is that a changing electric field makes a changing magnetic field.

→ displacement; → current.

An induced current circulating in masses of metal moving in a magnetic field or located in a changing magnetic field. Also known as → Foucault current.

→ eddy; → current.

The → rate at which → electric charge → flows past a given point through a → conductor, measured in → amperes.

→ electric; → current.

Same as → eddy current.

→ Foucault; → current.

The direct electric current that flows between metals or conductive nonmetals in a → galvanic couple.

→ galvanism; → current.

A cold ocean current that flows northward along the western side of South America, offshore Chile and Peru. Dominate weather in this area includes coastal fog and low clouds. The presence or lack of this current is a vital part of the weather pattern known as El Niño.

Named after the German naturalist and explorer Alexander von Humboldt (1769-1859). → current.

Current resulting from the relative motion of a conductor through a magnetic field.

→ induced ; → current.

A unidirectional electric current that flows and ceases to flow at irregular or regular intervals.

→ intermittent; → current.

The current produced in an → photoelectric effect process when → photoelectrons are received at the positive electrode.

→ photoelectric; → current.

Occurring or appearing again, especially repeatedly or periodically (Dictionary.com). → recurrence nova.

Verbal adj. from → recur.

A → cataclysmic variable star that undergoes → outbursts similar to those found in novae.

→ recurrent; → nova.