An Etymological Dictionary of Astronomy and Astrophysics
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The → counterpart of the → magnetic north pole. It lies near the → geographic north pole.

→ magnetic; → south; → pole.

Radiation emitted by a rotating magnet.

→ magnetic; → dipole; → radiation.

The direction of the Earth's axis at a particular epoch if the nutation is ignored.

→ mean; → pole.

An entity consisting of several poles.

→ multi-; → pole.

A variable used in → spherical harmonic expansions. Each spherical harmonic is characterized by its multipole index l: l = 0 for a → monopole, l = 1 for a → dipole, and so on. It is used in particular to describe the → cosmic microwave background anisotropy: ΔT/T₀ (θ,φ) = Σ a_lmY_lm(θ,φ), where θ and φ are the → spherical polar coordinates, Y_lm is the → spherical harmonic functions, and the sum runs over l = 1, 2, ..., ∞ and m = -l, ..., l, where the multipole index l corresponds to angular scales ≅ 180°/l.

→ multipole; → index.

The quantity that gives the electric potential field due to a distribution of charges, such as a → dipole, → quadrupole, → octupole, etc. A multipole moment usually involves powers of the distance to the origin, as well as some angular dependence.

→ multi-; → pole; → moment.

The point in the → northern hemisphere where the → rotation axis of Earth touches the → celestial sphere. The star → Polaris, also called the Pole Star, is located very near this point, at an angular separation of 42 degrees (about 1.4 lunar diameters).

→ north; → celestial; → pole.

1) An → imaginary → point in the → northern hemisphere representing the intersection of the → Earth's → rotation axis with the → globe or with the → celestial sphere.
2) For a → magnet, the pole which points toward the geographic north.
3) In a → magnetic field, the point from where a → line of force is leaves for the → south pole.

→ north; → pole.

A star that lies on the → rotation axis of the Earth in the north hemisphere. The → Pole Star is not, in the long term, permanently fixed to the → celestial pole. This is because of the Earth's → axial precession which gradually moves the celestial poles in the sky. It takes about 26,000 years for the precession to turn the pole a full circuit. Currently the North Pole Star is → Polaris, which will continue to mark the north celestial pole for several more centuries. But, around 4,000 B.C. → Gamma Cephei will become the North Pole Star. Around 7,500 B.C., → Alderamin will take up the role. And it will be the brilliant → Vega's (Alpha Lyrae) turn in about 12,000 years. In the past, about 3,000 B.C., → Thuban (Alpha Draconis) was the North Pole Star. Then → Kokab (Beta Ursae Majoris) became the Pole Star from 1500 B.C. to 500 A.D. before leaving the task to Polaris.

→ north; → pole; → star.

A → multipole consisting of eight point charges. Octupole moments are much smaller than → quadrupole moments and very much smaller than → dipole moment.

→ oct-; → pole.

1) Either extremity of the axis of the Earth or of any spherical body.
2) Either of the two regions or parts of an electric battery, magnet, or the like, at which the magnetic flux density is concentrated.
3) → pole of a mirror.
4) The fixed point in a system of polar coordinates that serves as the origin.

M.E., from L. polus "end of an axis, the sky," from Gk. polos "pivot, pole," polein "move around;" from PIE base *kwel- "to turn, move around, sojourn, dwell;" cognate with Pers. carx "every thing performing a circulatory motion; a wheel; a cart;" Av. caxra- "wheel," caraiti "he moves, approaches;" cf. Skt. cakra- "wheel, circle; cycle," carati "he moves, wanders;" Gk. kyklos "circle, wheel" (loaned L.L. cyclus); L. colere "to dwell in, to cultivate, move around," colonus "farmer, settler;" O.E. hweol "wheel;" Rus. koleso "wheel."

Qotb, from Ar. quTb.

The point where the → principal axis passes through the mirror.

→ pole; → mirror.

A star that lies along the Earth's → rotation axis. The term usually refers to the star → Polaris, which is the current → North Celestial Pole star. The → South Celestial Pole is not currently associated with any bright star. See also: → North Pole Star, → South Pole Star.

→ pole; → star.

A set of either two → electric dipoles or two → magnetic dipoles in close proximity to each other arranged with alternating polarities and acting as a single unit. Quadrupole interactions are much smaller than dipole interactions, but can allow transitions forbidden in dipole moment transitions.

From L. quadru-, variant of quadri- "four" + → pole, on the model of → dipole.

Cahâr, → four, + qotb, → pole + noun/nuance suffix -é.

The → anisotropy which is at the origin of the → cosmic microwave background polarization. The quadrupole anisotropy could arise from three types of perturbations: → scalar perturbation, → vector perturbation, and → tensor perturbation

→ quadrupole; → anisotropy.

A device, consisting of four → electrodes or → magnetic poles arranged in alternating → polarity, that focuses a beam of → charged particles.

→ quadrupole; → lens.

A quantity characterizing an electric charge distribution, determined by the product of the charge density, the second power of the distance from the origin, and a spherical harmonic over the charge distribution.

→ quadrupole; → moment.

The point in the → southern hemisphere where the → rotation axis of the Earth touches the → celestial sphere. In contrast to the → north celestial pole, no bright star is visible in that direction.

→ north; → celestial; → pole.

1) An → imaginary point in the → southern hemisphere representing the intersection of the → Earth's → rotation axis with the → globe with the → celestial sphere.
2) For a → magnet, the pole which points toward the geographic south.
3) In a → magnetic field, the point which receives a → line of force coming from the → north pole.

→ south; → pole.

A star that would mark the south → celestial pole. Presently no bright visible star is situated along the → rotation axis of the Earth in the southern hemisphere. But, because of the Earth's → axial precession, about 7,000 years from now the star → Delta Velorum in the constellation → Vela, the Sail, will come to within 0.2 degrees of the South Celestial Pole (around the year 9250 B.C.). That is closer to marking the celestial pole than → Polaris or → Sirius ever do during their reigns as pole stars! Sirius will become the South Pole Star some 60 thousand years from now (around the year 66270 B.C.). In that time, Sirius will come to within 1.6 degrees of the South Celestial Pole.

→ south; → celestial; → pole.