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

The concentric colored rings formed by an electrical → spark when a → discharge takes place on a metallic plate.

Joseph Priestley (1733-1804), English chemist, author, and clergyman; → ring.

1) First or highest in rank or importance; chief; principal.
2) Abbreviation for → primary body, → primary star, or → primary mirror.

M.E., from L. primarius "of the first rank, principal," from primus "first."

Naxostân, from naxost, from Mid.Pers. naxust "the first," Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx "beginning" + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

The body that is being orbited; such as the → Sun in the → solar system. As regards → multiple star systems, the most massive, or → primary star. See also: → secondary body.

→ primary; → body.

A → cell in which the electrochemical action producing the current is not normally reversible. Such a cell cannot be recharged by an electric current. → secondary cell.

→ primary; → cell.

The → cosmic rays which arrive on the Earth's → atmosphere from the outer space. The primary cosmic rays are very high energy → protons and to a lesser extent heavier nuclei which rain upon the Earth from all diretions in the outer space. They contain about 90% protons, 7% → alpha particles and about 1% still heavier nuclei of amost all the atoms from Li to Ni ( → mass number< 60). See also: → secondary cosmic rays.

→ primary; → cosmic; → ray.

Of a transiting → exoplanet, the event and the interval of time during which the planet passes in front of its host star. The planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet's limb. → secondary eclipse.

→ primary; → eclipse.

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

→ primary; → mirror.

The main rainbow that forms between about 40° and 42° from the → antisolar point (or about 50° from the → antisolar point), as viewed by the observer. The light path involves → refraction and a → single  → reflection inside the water → droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue.

As the droplets get smaller, red weakens.

Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the Sun is illuminating from the west.

→ primary; → rainbow.

In a → multiple star system, the most massive → component. In other words, the star nearest to the system's → center of garvity.

→ primary; → star .

1) Of the first importance; of the highest rank.
2) Same as → prime number.

M.E., from L. primarius "of the first rank, principal," from primus "first."

Naxost, naxostin, naxosti, from Mid.Pers. naxust "the first," Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx "beginning" + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

The focal point of a large primary reflecting mirror. This focus actually falls at a point just within the upper structure of the telescope and provides a large field of view.

→ primary; → focus.

The meridian at which longitude is defined to be 0°. The meridian running through Greenwich.

→ primary; → meridian.

A number which is divisible by no whole number other than itself and one.

→ prime; → number.

The great circle through the observer's zenith that intersects the horizon at the west and east points. → vertical circle.

→ primary; → vertical.

Lemaître's (1931) name for the early dense Universe, which later became known as the → Big Bang theory.

From L. primaevus "early in life," from primus "first," → prime, + aevum "an age," + → -al; → atom.

Pertaining to or existing at or from the very beginning.

From L.L. primordialis "first of all, original," from L. primordium "the beginning," from primus "first" + stem of ordiri "to begin."

Bonâqâzin, from bon "basis; root; foundation; bottom" (Mid.Pers. bun "root; foundation; beginning," Av. būna- "base, depth," cf. Skt. bundha-, budhná- "base, bottom," Pali bunda- "root of tree") + âqâzin "pertaining to the beginning," from âqâz "beginning" (Proto-Iranian *āgāza-, from prefix ā- + *gāz- "to take, receive," cf. Sogdian āγāz "beginning, start," pcγz "reception, taking").

The relative amount of a light element (e.g. deuterium, lithium, helium) synthesized in the early Universe.

→ primordial; → abundance.

A black hole formed following the Big Bang event due to incredibly violent turbulence that squeezed concentrations of matter to high densities. These black holes, first suggested by Stephen Hawking, are expected to have a mass comparable to that of a mountain and a size as small as an atom. Same as → mini black hole.

→ primordial; → black hole.

In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.

→ primordial; → curvature; → perturbation.

A high redshift, metal-deficient galaxy that formed very early in the history of the Universe.

→ primordial; → galaxy.