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

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 66°33' N or S) to 179 days at the North/South Pole.

→ polar; → day.

A spacecraft orbit that passes over, or close to, the geographic poles of the Earth or some other solar system object.

→ polar; → orbit.

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.

→ polar; → orbit; → satellite.

A coronal feature of the Sun, which appears as long, thin streamers that project outward from the Sun's north and south poles

→ polar; → plume.

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.
2) One of the two main wind components in → B[e] stars. The pole is hotter than the equator due to the → gravity darkening effect leading to a relatively fast, low-density wind driven by Fe IV lines. The other component is the → equatorial wind. The mechanism put forward to explain this wind morphology is the rotationally induced → bistability mechanism.
3) An extremely cold wind blowing from the north or south polar regions of the Earth.

→ polar; → wind.

Of or relating to → polarimetry.

→ polarimetry; → -ic.

The measurement of the → polarization state of light, usually through the use of a polarimeter.

From polari, from → polarization + → -metry.

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.
Jodey, from Ar. Judaiy.
Mix-e gâh, Mid.Pers. name of the star, literally "the nail (peg) of time/place," from mix, → nail, + gâh "time; place," → origin.

1) Physics: The condition, in a system, of having opposite characteristics at different points, especially positive or negative with respect to electric charge or magnetic properties.
2) Chemistry: A property of a molecule caused by unsymmetrical charge distribution.

From → polar + → -ity.

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.

→ polarity; → epoch.

A specific event in the history of Earth's magnetic field. Usually used in reference to a specific → polarity reversal.

→ polarity; → event.

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.
2) The change in the polarity of the → solar magnetic field with the ending of each → solar activity cycle so that the North magnetic pole becomes the South and vice versa.

→ polarity; → reversal.

Able to be polarized.

→ polaize; → -able.

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.
2) Electricity: A process or state in which the → dipole moments of → polar molecules in a → dielectric material get aligned under the action of an external electric field. Actually thin layers of bound charges with opposite signs appear on the surfaces of the dielectric.
3) Electricity: The accumulation of ions, produced during electrolysis, on the electrodes of a cell, increasing the resistance of the cell.

Verbal noun of → polarize.

Same as → polarizing angle and → Brewster angle.

→ polarization; → angle.

Same as → bound charge.

→ polarization; → charge.

→ degree of polarization.

→ polarization; → degree.

The ratio expressed by P = (I_par - I_per) / (I_par + I_per), where I_par and I_per are the light intensities with the electric field vector respectively parallel and perpendicular to the incident beam.

→ polarization; → fraction.

To cause → polarization. To undergo polarization.

Infinitive of → polarization.

Of or pertaining to a medium or physical phenomenon that exhibits → polarization.

P.p. of → polarize.