Fr.: équation polaire
An equation for a curve written in terms of the → polar coordinates.
Fr.: facules polaires
Solar faculae occurring in regions of high heliographic latitudes. They are smaller than the main-zone faculae; their shape is point-like or oval. Their lifetimes range from a few minutes to some hours, but the decisive difference from the main-zone faculae lies in their activity cycle. When spots and faculae of the main zone are at minimum, the polar faculae have their maximum activity, and vice versa.
Fr.: molécule polaire
A molecule in which the centers of positive and negative charge distribution do not converge and therefore has a mostly positive charge on one side and a mostly negative charge on the other. Different atoms around a central atom will always be polar molecules. Some polar molecules are H2O, HF, COS, and CH3Cl. Polar molecules are characterized by a → dipole moment.
Fr.: mouvement du pÃ´le
The irregularly varying motion of the Earth's pole of rotation with respect to the Earth's crust.
Fr.: nuit polaire
In polar regions, the portion of the year when the Sun does not rise above the horizon. Its length changes from twenty hours at the Arctic/Antarctic Circle (latitude 66Â°33' N or S) to 179 days at the North/South Pole.
madâr-e qotbi (#)
Fr.: orbite polaire
A spacecraft orbit that passes over, or close to, the geographic poles of the Earth or some other solar system object.
polar orbiting satellite
mâhvâré bâ madâr-e qotbi
Fr.: satellite en orbite polaire
A satellite that revolves around the Earth in an almost north-south orbit, passing close to both poles. The orbits are sun synchronous, allowing the satellite to cross the equator at the same local time each day. These satellites orbit at a height of 830-880 km and take about 100 minutes to complete a turn around the Earth.
Fr.: plume polaire
A coronal feature of the Sun, which appears as long, thin streamers that project outward from the Sun's north and south poles
Fr.: vent polaire
1) The → solar wind occurring at high latitudes during low
→ solar activity as a fast
(around 750 km s-1) and relatively
steady flow. A remarkable feature of the polar wind is the ubiquitous presence of
an intense flow of → Alfvénic fluctuations.
Of or relating to → polarimetry.
The measurement of the → polarization state of light, usually through the use of a polarimeter.
setâre-ye qotbi, jodey, mix-e gâh
Fr.: étoile polaire
The brightest star associated with the → north celestial pole. Polaris, also called the Pole Star, is a → triple system lying at about 433 → light-years (133 → parsecs) from the Earth. It is not exactly located on the Earth → rotation axis, because an → angular distance of 42 arc-minutes (about 1.4 lunar diameter) separates it from the true north pole. The main star, Polaris Aa (→ visual magnitude about 2), is a variable → pulsating star of type → Cepheid. It is a hot, blue F7 Ib → supergiant star having a → luminosity about 1,260 times that of the Sun. It has a mass of 5.4 Msun, a radius of 37.5 Rsun, and a → surface temperature of 6,015 K. The close companion Ab (apparent magnitude 9.2) is only 0''.17 (about 18.5 → astronomical units) from Polaris A. It was discovered in 1929 through examining the spectrum of Polaris A. It orbits Aa every 29.59 years. Ab is a → main sequence star of → spectral type F6 V. It has a mass of 1.26 Msun, a radius of 1.04 Rsun, and a luminosity of 3 Lsun. The third component, Polaris B (visual magnitude 8.7), is separated from A by 18.2 arc sec, corresponding to approximately 2,400 AU. It was first noticed by William Herschel in 1780. Polaris B is a main sequence star of type F3 V with a mass 1.39 Msun, a radius 1.8 Rsun, a luminosity of 3.9 Lsun, and a surface temperature of 6,900 K. Due to the → precession of equinoxes, the direction that Earth's axis points at changes slowly with time. Hence, Polaris has not always been, nor will it always be, the Pole Star. Polaris is actually drawing closer to the pole and in 2100 it will be as close to it as it ever will come, just 27.15 arc-minutes or slightly less than the Moon's apparent diameter. It will continue its reign as the North Star for many centuries to come. Historically, around 400 B.C., during Plato's time the nearest star to the Pole star was → Kochab (β Ursae Minoris). Some 4,600 years ago, when the Egyptians constructed the Pyramids, the Pole star was → Thuban (α Draconis). In 2,000 years the star → Errai (γ Cephei) will become the Pole Star. And around the year 14,000, Earth's axis will point reasonably close to the star → Vega, the fifth brightest star in the sky.
Mod.L. short for stella polaris "the pole star," → polar.
Setâre-ye qotbi "polar star," from setâré,
→ star, + qotbi, → polar.
1) Physics: The condition, in a system, of having opposite characteristics at
different points, especially positive or negative with respect to electric charge or
Fr.: époque de polarité
The time during which the Earth's magnetic field was of a single polarity; an interval of time between reversals of Earth's magnetic field.
Fr.: événement de polarité
A specific event in the history of Earth's magnetic field. Usually used in reference to a specific → polarity reversal.
v âruneš-e qotbigi, vâgardâni-ye ~
Fr.: inversion de polarité
1) A change in the → polarity of Earth's magnetic field
in which the north magnetic pole becomes the south magnetic pole and vice versa.
Also known as geomagnetic reversal or magnetic reversal. Earth's magnetic
field has reversed many times in the past and the time intervals
between these changes are known as → polarity epochs.
Able to be polarized.
1) Optics: A process or state in which the directions of the electric or magnetic fields
of an → electromagnetic radiation
change in a regular pattern. Light can be polarized by a
variety of ways, involving the following processes: reflection, transmission,
double refraction, and scattering. See also
→ unpolarized light;
→ linear polarization;
→ circular polarization;
→ elliptical polarization.
The study of the polarization of light from astronomical sources can yield
unique information in particular related to the properties of magnetic fields.
Verbal noun of → polarize.
zâviye-ye qotbeš (#)
Fr.: angle de polarisation
Same as → bound charge.