An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < axi rot she > >>

Number of Results: 47 Search : rotation
axis of rotation
  آسه‌ی ِ چرخش   
âse-ye carxeš

Fr.: axe de rotation   

Same as → rotation axis and → rotational axis.

axis; → rotation.

Carrington rotation
  چرخش ِ کرینگتون   
carxeš-e Carrington

Fr.: rotation de Carrington   

A system for counting rotations of the Sun based on the mean → synodic rotation period of the Sun. Initially, Lord Carrington determined the solar rotation rate by watching low-latitude → sunspots. He defined a fixed solar coordinate system that rotates in a sidereal frame exactly once every 25.38 days. This means that the solar rotation period, as viewed from the Earth, is assumed to be constant. However, the synodic rotation rate varies during the year because of the changing speed of the Earth in its orbit and the mean synodic period is about 27.2753 days. Carrington rotation number 1 began on November 9, 1853.

Named for Richard C. Harrington (1826-1875), British astronomer, who initiated the system; → rotation.


Fr.: corotation   

The act of corotating.

Verbal noun of → corotate.

corotation radius
  شعاع ِ هم‌چرخش   
šoâ'-e ham-carxeš

Fr.: rayon de corotation   

1) In the → X-wind model of → accretion, the distance from the star where the → centrifugal force on a particle corotating with the star balances the → gravitational attraction; in other words, where the → accretion disk rotates at the same → angular velocity as the star.
2) In a → spiral galaxy, the place where the spiral → pattern speed has the same velocity as the → rotation curve of the → galactic disk. In the frame rotating with the wave, particles inside this radius will appear to revolve in the direction of the frame rotation (prograde) while outside this corotation radius, they will be retrograde.

corotation; → radius.

corotation resonance
  باز‌آوایی ِ هم‌چرخش   
bâzâvâyi-ye ham-carxeš

Fr.: résonance de corotation   

That condition of a → galactic disk at an orbital radius in which the → angular velocity of the disk equals the → pattern speed. It is significant that the spiral wave pattern rotates as a rigid body (ΩP = const), whereas the galactic disk rotates differentially (Ω is a function of galactocentric distance r). The distance rC at which the two angular velocities coincide (Ω(rC) = ΩP) is referred to as the → corotation radius. The corotation resonance and its position within the galaxy is one of the fundamental properties of a spiral galaxy.

corotation; → resonance.


Fr.: dextrorotation   


dextro-; → rotation.

differential rotation
  چرخش ِ دگرسانه‌ای   
carxeš-e degarsâneyi

Fr.: rotation différentielle   

1) Of a single body (such as a star or a gaseous planet), the axial rotation of equatorial latitudes faster than polar latitudes.
2) Of a galaxy, the orbiting of stars nearer the center faster than those at the edge.

differential; → rotation.

Earth's rotation
  چرخش ِ زمین   
carxeš-e zamin (#)

Fr.: rotation de la Terre   

The natural motion of the Earth around its own axis, which takes place once in a → sidereal day. The Earth rotates toward the → east, in the same direction as it revolves around the Sun. If viewed from the north celestial pole, the Earth turns → counterclockwise. The opposite is true when the Earth is viewed from the south celestial pole. The Earth's rotation is responsible for the diurnal cycles of day and night, and also causes the apparent movement of the Sun across the sky. The Earth's rotation velocity at the → equator is 1,673 km h-1 or about 465 m s-1. More generally, at the → latitude  φ it is given by: vφ = veq cos φ, where veq is the rotation velocity at the equator. The Earth's rotation is gradually slowing down under the action of the → tides, which are generated by the → gravitational attraction of the → Moon. As the result of this → tidal friction, the day is becoming longer at a rate of about 2 milliseconds, or 0.002 seconds, per century (or one second every 50,000 years). Moreover, the loss of the Earth's → rotational angular momentum increases the Moon's → orbital angular momentum, because the angular momentum of the → Earth-Moon system is conserved. In consequence, the Moon slowly recedes from the Earth by about 4 cm per year, which leads to increasing its orbital period and the length of a month as well.

Earth; → rotation.

Faraday rotation
  چرخش ِ فارادی   
carxeš-e Faraday (#)

Fr.: rotation Faraday   


farad; → rotation.

field rotation
  چرخش ِ میدان   
carxeš-e meydân

Fr.: rotation de champ   

The effect of the Earth's rotation on the position of the image formed on the → focal plane of a telescope during long exposures. In the case of → equatorial mounting, the image remains fixed, whereas it turns continuously with an → altazimuth mounting. In the latter case the image motion must be compensated by an appropriate mechanism, → field rotator.

field; → rotation.

flat rotation curve
  خم ِ چرخش ِ تخت   
xam-e carxeš-e taxt

Fr.: courbe de rotation plate   


flat; → rotation; → curve.

galactic rotation
  چرخش ِ کهکشان   
carxeš-e kahkešân

Fr.: rotation galactique   

The revolving of the gaseous and stellar content of a galaxy around its central nucleus. The rotation is not uniform, but differential. One revolution of the Sun within our own Galaxy takes about 220 million years, or one cosmic year.

galactic; → rotation.

Keplerian rotation curve
  خم ِ چرخش ِ کپلری   
xam-e carxeš-e Kepleri (#)

Fr.: courbe de rotation keplérienne   

A → rotation curve in which the speed of the orbiting body is inversely proportional to the → square root of its distance from the mass concentrated at the center of the system.

Keplerian; → rotation; → curve.


Fr.: lévorotation   

The counterclockwise rotation of the → plane of polarization of light (as observed when looking straight through the incoming light) by certain substances.

Adj. related to → levorotation.

lunar rotation
  چرخش ِ مانگ   
carxeš-e mâng

Fr.: rotation de la Lune   

The Moon's motion around its axis, which takes place in 27.321 661 days (→ sidereal month). Since the Moon and the Earth are → tidally locked our satellite has a → synchronous rotation. This means that it rotates once on its axis in the same length of time it takes to revolve around Earth. That is why the Moon always shows the same face to us. However, over time we can see up to 59 percent of the lunar surface because the Moon does not orbit at a constant speed (→ libration in longitude) and its axis is not perpendicular to its orbit (→ libration in latitude). The Moon also creates tides in Earth oceans. As the Earth rotates, the rising and falling sea waters bring about friction within the liquid itself and between the water and solid Earth. This removes energy from Earth's rotation and causes it to spin more slowly. As a result, days are getting longer, at about 2 milliseconds per century. On the other hand, since the → angular momentum of the → Earth-Moon system must be conserved, the Moon gradually moves away from the Earth. This, in turn, requires its orbital period to increase and, because the Moon is tidally locked to Earth, to spin more slowly.

lunar; → rotation.

magnetorotational instability (MRI)
  ناپایداری ِ مغنات-و-چرخشی   
nâpâydâri-ye meqnâtocarxeši

Fr.: instabilité magnétorotationnelle   


magneto-; → rotational; → instability.

plane of rotation
  هامن ِ چرخش   
hâmon-e carxeš

Fr.: plan de rotation   

For a rotating object, the plane → perpendicular to the → rotation axis.

plane; → rotation.

projected rotational velocity
  تندای چرخشی ِ فراشانده   
tondâ-ye carxeši-ye farâšândé

Fr.: vitesse rotationnelle projetée   



carxeš (#)

Fr.: rotation   

The motion of a body about its axis.

Verbal noun of → rotate.

rotation axis
  آسه‌ی ِ چرخش   
âse-ye carxeš

Fr.: axe de rotation   

The imaginary line around which an object rotates. Same as → rotational axis and → axis of rotation.

rotation; → axis.

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