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

Of the → cosmic microwave background radiation, a plot of how much the temperature varies from point to point on the sky versus the angular frequency. This spectrum answers fundamental questions about the nature of the Universe. → cosmic microwave background anisotropy; → dipole anisotropy.

→ angular; → power; → spectrum.

A plot displaying the amplitude of → cosmic microwave background anisotropy as a function of angular size or → multipole index. Same as → angular fluctuation spectrum. The plot, based the on WMAP and other data, shows a plateau at large angular or length scales (→ Sachs-Wolfe plateau), then a series of peaks at progressively smaller scales. These features arise from the gravity-driven acoustic oscillations of the coupled photon-baryon fluid in the early Universe (→ baryon acoustic oscillation). In particular, a strong peak is seen on an angular scale (at l ~220), corresponding to the physical length of the → sound horizon at the → recombination era. It depends on the curvature of space. If space is positively curved, then this sound horizon scale will appear larger on the sky than in a flat Universe (the first peak will move to the left). The second peak (l ~ 550), which is the first harmonic of the main peak, relates to the baryon/photon ratio. The third peak can be used to help constrain the total matter density.

→ angular; → fluctuation; → spectrum.

A measure of the ability of a medium to separate different colors of light. It is defined by: (n₂ - n₁)/(n - 1), where  n₁ and n₂ are refractive indices at two specified widely differing wavelengths, and n is the → index of refraction for the average of these wavelengths.

→ dispersive; → power.

The energy emitted from unit surface area of body per second.

→ emissive; → power.

The angle between extreme points of the main lobe of an antenna pattern where the sensitivity of the antenna is half the value at the center of the lobe. This is the nominal resolving power of the antenna system.

→ half; → power; → beam; → width.

A laser beam with the output power in the range 10¹²-10¹⁵ watts/cm², capable of depositing kilo-joule order energies during nano-second time intervals in small volumes (about 1 mm³). High power lasers, which can produce temperatures of 10-50 million degrees and pressures of 10-100 million bars, are used to simulate astrophysical conditions in laboratories.

→ high; → power;, → laser.

leyzer, → laser; por "much, many, full," → full; tavân, → power.

A unit that is used to measure the → power of engines and motors.
1) Metric horsepower is equal to the power required to carry a load of 75 kg over a distance of one meter in one second. It is equivalent to 746 → watts.
2) British (US) horsepower is the rate of work when 33,000 foot-pounds of work are done per minute. The horsepower was defined by James Watt (1736-1819), the inventor of the steam engine, to compare the output of steam engines with the power of draft horses. He determined that a horse is typically capable of a power of 550 foot-pounds per second.

→ horse; → power.

Asb-e boxâr "vapor horse," translation of Fr. cheval-vapeur, from asb, → horse, + boxâr, → vapor.

The most important function of an astronomical telescope, which is directly related to the area (or to the square of the diameter) of the main mirror or lens.

→ light; gathering, from O.E. gadrian, gædrian "to gather, collect;" → power.

Tavân, → power; gerdâvari, verbal noun of gerd âvardan, from gerd "round; around" (Mid.Pers. girt "round, all around," O.Iranian *gart- "to twist, to wreathe," cf. Skt. krt "to twist threads, spin, to wind, to surround," kata- "a twist of straw;" Pali kata- "ring, bracelet;" Gk. kartalos "a kind of basket," kyrtos "curved") + âvardan "to bring," Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring, to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry;" nur, → light.

The ratio between the focal lengths of the objective and ocular in a telescope.

Magnifying, verbal adj. of → magnify; → power.

The → rate at which → work is done by a → force. In other words, → mechanical energy per unit time. Mechanical power is expressed in units of joules/sec (joules/s) or a watt (W) in the → mks system.

→ mechanical; → power.

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.

Electric or motive power whose primary source is nuclear energy.

→ nuclear; → power.

A → positive integer that can be expressed as an integer → power of another positive → integer. For example, n is a perfect power if there exist natural numbers m> 1, and k> 1 such that m^k = n. → perfect cube, → perfect square.

→ perfect; → power.

1) Physics: The → rate of doing → work on transferring → energy, as expressed in ergs/sec, watts, etc. Same as → mechanical power.
2) Math.: An → exponent to which a given quantity is raised. The expression xⁿ is therefore known as "x to the n-th power."

M.E. pouer(e), poer(e), from O.Fr. povoir, noun use of the infinitive in O.Fr., "to be able," from V.L. *potere, from L. potis "powerful, able, capable;" cognate with Av. paiti- "lord, husband;" Mod.Pers. -bad (sepah-bad "general, commander of an army"); Skt. pái- "master, husband;" Gk. posis "husband;" Lith. patis "husband."

Tavân "power, strength," tavânestan "to be powerful, able;" Mid.Pers. tuwan "power, might," from O.Pers./Av. base tav- "to have power, to be strong, to be able," Av. tavah- "power," təviši- "strength," Mod.Pers. tuš, tâb "power, ability," O.Pers. tauman- "power, strength," tunuvant- "powerful," Skt. tu- "to be strong, to have authority," tavas-, tavisa- "strong, energetic," tavisi- "power, strength."

A function of the form f(x) = xⁿ, where n is a → real number.

→ power; → function.

A mathematical relationship between two quantities expressed by a → power function.

→ power; → law.

A series in which the terms contain regularly increasing powers of a variable. In general, a₀ + a₁x + a₂x² + ... + a_nxⁿ, where a₀, a₁, etc. are constants.

→ power; → series.

Same as → spectral density.

→ power; → spectral; → density.

The plot that gives the portion of a signal's power falling within given frequency bins. The most common way of generating a power spectrum is by using a discrete Fourier transform.

→ power; → spectrum.

For a → random variable X, any → distribution which has the form: P(X ≥ x) = (k/x)^α, where x is a value in the range defined for X, k > 0 is a parameter termed location parameter, and α > 0 is the → slope parameter.

→ power; → law; → distribution.