An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 95 Search : law
dynamical law
  قانون ِ توانیک   
qânun-e tavânik

Fr.: loi dynamique   

A law that describes the motion of individual particles in a system, in contrast to → statistical laws.

dynamical; → law.

Faraday's law of induction
  قانون ِ درهازش ِ فارادی   
qânun-e darhazeš-e Faraday

Fr.: loi d'induction de Faraday   

The induced → electromotive force in a circuit is equal in magnitude and opposite in sign to the rate of change of the → magnetic flux through the surface bounded by the circuit. Mathematically, it is expressed as: ∇ x E = -∂B/∂t, which is one of the four → Maxwell's equations.

farad; → law; → induction.

Fechner's law
  قانون ِ فشنر   
qânun-e Fechner (#)

Fr.: loi de Fechner   

See → Weber-Fechner law.

first law of thermodynamics
  قانون ِ نخست ِ گرماتوانیک   
qânun-e naxost-e garâtavânik

Fr.: première loi de la thermodynamique   

The total energy of a → closed system is constant. This means that energy can be changed from one form to another, or transferred from one system to another, but it cannot be created or destroyed. A mathematical formulation of the first law is: δQ = δU + δW, where δQ is the heat transferred to the system, δU the change in internal energy (resulting in a rise or fall of temperature), and δW is the work done by the system.

first; → law; → thermodynamics.

Freeman's law
  قانون ِ فریمن   
qânun-e Freeman

Fr.: loi de Freeman   

A statistical finding about "normal" → spiral galaxies, whereby there is an upper limit on the mean central → surface brightness of disks. This value is constant for different spiral types, amounting to 21.65 ± 0.30 mag arcsec2 in the B band.

Named after K. C. Freeman (1970, Ap.J. 160, 811); → law.

Galileo's law of falling bodies
  قانون ِ گالیله درباره‌ی ِ افت ِ جسم‌ها   
qânun-e Gâlilé darbâre-ye oft-e jesmhâ

Fr.: loi galiléenne de la chute des corps   

In the absence of air resistance, any two bodies that are dropped from rest at the same moment will reach the ground at the same time regardless of their mass.

Galileo (1564-1642) was the first to determine, at the start of the seventeenth century, the law of constant acceleration of free-falling bodies. → law; → fall; → body.

Gauss's law for electricity
  قانون ِ گاؤس در برق   
qânun-e Gauss dar barq

Fr.: loi de Gauss en électricité   

The total electric flux ψ out of an arbitrary closed surface in free space is equal to the net charge within the surface divided by the → permittivity. In differential form: ∇ . E = ρ/ε0, where ρ is the → charge density and ε0 the permittivity. The integral form of the law: ∫E . dS = Q0 (closed surface integral). This is one of the four → Maxwell's equations.

gauss; → law; → electricity.

Gauss's law for magnetism
  قانون ِ گاؤس در مغنات‌مندی   
qânun-e Gauss dar meqnâtmandi

Fr.: loi de Gauss en magnétisme   

The → magnetic flux through an arbitrary closed surface equals zero. Mathematically, in differential form: ∇ . B = 0 and in integral form: ΦB = ∫B.dS = 0 (closed surface integral). This is one of the four → Maxwell's equations. This law expresses the fact that there are no free magnetic poles (→ monopoles) in nature and that all the lines of force of a magnetic field are closed curves.

gauss; → law; → magnetism.

Gay-Lussac's law
  قانون ِ گی-لوساک   
qânun-e Gay-Lussac (#)

Fr.: loi de Gay-Lussac   

1) Law of combining volumes. The volumes of gases used and produced in a chemical reaction, are in the ratio of small whole numbers when measured at constant temperature and pressure.
2) For a gas held at constant volume, there is a direct correlation between temperature and pressure: P1/T1 = P2/T2. Gay-Lussac's law, → Boyle-Mariotte law, and → Charles' law were later unified into the → ideal gas law.

Named after Joseph Louis Gay-Lussac (1778-1850), a French chemist and physicist; → law.

Hale's law
  قانون ِ هیل   
qânun-e Hale

Fr.: loi de Hale   

The leader and → follower spots have opposite polarities on either side of the equator. This reverses after the ~11 year → solar cycle. Also called Hale-Nicholson's law.

Named after George Ellery Hale (1868-1938), American astronomer; → law.

Hooke's law
  قانون ِ هوک   
qânun-e Hooke (#)

Fr.: loi de Hooke   

The law stating that if a body is deformed the → strain produced is directly proportional to the applied → stress. If the elastic limit is not exceeded, the material returns to its original shape and size on the removal of the stress. Hooke's law forms the basis of the theory of → elasticity.
More specifically, within certain limits, the force required to stretch an elastic object such as a metal spring is directly proportional to the extension of the spring. It is commonly written: F = -kx, where F is the force, x is the length of extension/compression and k is a constant of proportionality known as the spring constant.

Named after Robert Hooke (1635-1703), British scientist who described the relationship in 1676; → law.

Hubble law
  قانون ِ هابل   
qânun-e Hubble

Fr.: loi de Hubble   

Hubble-Lemaitre law.

Hubble; → law.

Hubble-Lemaitre law
  قانون ِ هابل-لومتر   
qânun-e Hubble-Lamaître

Fr.: loi de Hubble-Lemaître   

The speed with which a → galaxy cluster recedes from us is directly proportional to its distance. It can be stated as v = H0d, where v is the recessional velocity, H0 the → Hubble-Lamaitre constant, and d the distance. See also → Hubble-Lemaitre flow. It should be underlined that Hubble was not the first to discover the → velocity-distance relation. Two years before Hubble, in 1927, Georges Lemaître (1894-1966) had derived the relation and published it in a paper in French which remained neglected (→ Friedmann-Lemaitre Universe).

The International Astronomical Union (IAU) at its 30th Meeting approved the Resolution B4 proposed by the IAU Executive Committee recommending the use of Hubble-Lemaitre law instead of Hubble's law, after Edwin Hubble (1889-1953), the American astronomer who published his results in 1929 and Georges Lemaître, Belgian priest and astronomer, who published a paper on the expansion of the Universe in 1927; → law.

ideal gas law
  قانون ِ گاز ِ آرمانی، ~ ~ مینه‌وار   
qânun-e gâz-e ârmâni, ~ ~ minevâr

Fr.: loi des gaz parfaits   

An → equation of state that relates pressure (P), temperature (T), and volume (V) of an ideal or → perfect gas: PV = nRT, where n is the number of → moles of gas present and R is the → universal gas constant. Equivalently: PV = NkT, where N is the number of atoms of gas present and k is → Boltzmann's constant.

ideal; → gas; → law.

inverse square law
  قانون ِ توان ِ دوی ِ وارون، قانون ِ چاروش ِ وارون   
qânun-e tavân-e do-ye vârun, qânun-e câruš-e vârun

Fr.: loi en carré inverse   

A force law that applies to the → gravitational and → electromagnetic forces in which the magnitude of the force decreases in proportion to the inverse of the square of the → distance.

inverse; → square; → law.

Joy's law
  قانون ِ جوی   
qânun-e Joy

Fr.: loi de Joy   

Sunspot pairs or groups are tilted with the → leader spots closer to the equator than the → follower spots. The tilt of bipolar sunspot pairs increases with latitude.

Alfred Harrison Joy (1882-1973), an American astronomer; → law.

Kepler's first law
  قانون ِ نخست ِ کپلر   
qânun-e naxost-e Kepler (#)

Fr.: première loi de Kepler   

Planets move in elliptical paths, with the Sun at one focus of the ellipse (year 1609).

Kepler; → first; → law.

Kepler's laws
  قانون‌های ِ کپلر   
qânunhâ-ye Kepler (#)

Fr.: lois de Kepler   

1) The planets move about the Sun in ellipses, at one focus of which the Sun is situated.
2) The → radius vector joining each planet with the Sun describes equal areas in equal times.
3) The ratio of the square of the planet's period of revolution to the cube of the planet's mean distance from the Sun is the same for all planets.

Kepler; → law.

Kepler's second law
  قانون ِ دوم ِ کپلر   
qânun-e dovom-e Kepler (#)

Fr.: deuxième loi de Kepler   

A line joining a planet to the Sun sweeps out equal areas in equal intervals of time (year 1609).

Kepler; → second; → law.

Kepler's third law
  قانون ِ سوم ِ کپلر   
qânun-e sevom-e Kepler (#)

Fr.: troisième loi de Kepler   

The ratio between the square of a planet's → orbital period (P) to the cube of the mean distance from the Sun (a) is the same for all planets: P2a3 (year 1618). More accurately, P2 = (4π2a3) / [G(M1 + M2)], where M1 and M2 are the masses of the two orbiting objects in → solar masses and G is the → gravitational constant. In our solar system M1 = 1. The → semi-major axis size (a is expressed in → astronomical units and the period (P) is measured in years.

Kepler; → third; → law.

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