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

A suffix indicating a slope, as in → barocline, → thermocline, → tachocline.

Back formation from incline, → inclination.

Šib, → slope.

The → emission line of → neutral hydrogen in → interstellar clouds. It lies in the → radio spectrum at → wavelength of about 21 cm, → frequency 1420 MHz. Its existence was predicted by Hendrik van de Hulst in 1944 and discovered by Harold Ewen and Edward Purcell in 1951.

Twenty-one (21); → twenty + → one; → centimeter; → line.

The → emission line of → neutral hydrogen in interstellar clouds. It lies in the radio spectrum at wavelength of about 21 cm, frequency 1420 MHz. Its existence was predicted by Hendrik van de Hulst in 1944 and discovered by Harold Ewen and Edward Purcell in 1951.

Twenty-one (21); → twenty + → one; → centimeter; → line.

A dark line in the spectrum of a source produced by a lower temperature gas cloud lying between the source and the observer.

→ absorption; → line.

A spectral line produced by an → alkali metal.

→ alkali; → line.

Having the properties of an → alkali; having a → pH greater than 7.0.

From alkal(i) + -ine a suffix denoting "of or pertaining to," "of the nature of," "like."

From qalyâ, → alkali, + -yi adj. suffix.

Any of the metallic chemical elements belonging to group 2 of the → periodic table; i.e. → beryllium, → magnesium, → calcium, → strontium, → barium, and → radium. They are not found free in the nature because they are highly reactive.

→ alkaline; → earth; → metal.

Felez, → metal; qalyâyi, → alkaline; xâki "of or pertaining to soil," from xâk, → soil.

The line connecting the two apsides, i.e. the major axis of an elliptical orbit. → apsis.

Apsides, pl. of → apside; → line.

1) A prominent → forbidden line in the spectra of the aurora at wavelengths of 5577 and 6300 Å giving the aurora its characteristic green and red colors. Both are emitted by atomic oxygen, the former in its transition from the second lowest excited electronic state (¹S) to the lowest excited electronic state (¹D), the latter in its transition from the lowest excited electronic state (¹D) to the atomic ground state (³P).
2) A forbidden line emitted by interstellar ionized gas by several atomic species (O, O⁺, O⁺⁺, N⁺, S⁺⁺, etc.) corresponding to the transition from the state ¹S to ¹D. → forbidden line; → nebular line; → transauroral line.

→ auroral; → line.

The → spectral lines making up the → Balmer series.

→ Balmer; → line.

1) In radio interferometry, the separation between the electrical, or phase centers of two interferometer elements.
2) In spectroscopy, the contribution to a spectrum from phenomena that are not of astronomical interest, such as frequency dependent properties of the receivers, or by astronomical sources other than those under study.

→ base; → line.

The path in the → H-R diagram that continuously → accreting stars follow. Stars on the birthline are difficult to observe, because they are hidden by the → accretion disk and a dense → cocoon of → interstellar matter. The star becomes visible once a sufficient amount of the surrounding matter has been dispersed. It follows that the young starsare observed generally between the birthline and the → zero-age main sequence (ZAMS). Before hydrogen ignition, gravitational contraction and deuterium burning are the main energy sources for the star. The localization of the birthline depends on the deuterium → accretion rate. First introduced by R. Behrend & A. Maeder, 2001 (A&A 373, 190).

→ birth; → line.

→ Spectral lines intermingled.

→ blend; → line.

A radio galaxy that shows broad optical emission lines. → broad-line region.

→ broad; → line; → radio galaxy.

The inner region of a → quasar or an → active galactic nucleus exhibiting broad → spectral lines which indicate ionized matter moving with speeds in excess of 10,000 km sec^-1, probably due to the presence of an → accretion disk surrounding a → supermassive black hole. Also called Type I AGN. See also → obscuring torus.

→ broad; → line; → region.

A system of connected line → segments joined end to end.

Past participle of → break; → line.

Lying on the same straight line. Collinear points are a set of points on the same line.

→ com- + → linear.

A system of two or more forces that lie along the same → line of action.

→ collinear; → force.

A mathematical property where all points lying on a line initially still lie on a line after transformation.

→ collinear; → -ity.

Two line segments if they have the same length. They need not lie at the same angle or position on the plane.

→ congruent; → line; → segment.