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

A → forbidden line in → emission.

→ forbidden; → emission; → line.

A spectral line emitted by atoms undergoing energy transitions not normally allowed by the → selection rules of → quantum mechanics. Forbidden emission lines form in low-density interstellar gas and are collisionally excited. They are designated by enclosing in brackets, e.g. [O III] and [N II], O and N representing oxygen and nitrogen atoms respectively.

→ forbidden; → line.

One of many absorption lines and bands in the spectrum of the Sun. The most prominent features are labeled with capital letters A to K, starting at the red end. The A and B bands are now known to be caused by absorption in Earth's atmosphere, while the rest are due to absorption in the Sun's → photosphere. C and F are now better known as H-alpha and H-beta (→ Balmer series); the → D lines are of sodium, the → H and K lines of calcium, and the G band of neutral iron and the interstellar → CH (methylidine) molecule.

Named after Joseph von Fraunhofer (1787-1826), German optician and physicist, who discovered these lines in 1814; → line.

A → magnetic field line in a → fluid when the motion of the fluid carries the magnetic field along with it.

Frozen, p.p. of → freeze; → magnetic; → line.

The shortest line between two points on a surface. Also called → geodesic.

→ geodesic; → line.

Two prominent → absorption lines, at 3968.5 Å and 3933.7 Å respectively, in the spectra of stars like the → Sun and cooler due to → singly ionized → calcium (Ca II). The strength of H and K lines can be an indication of considerable magnetic activity in the → chromosphere of these stars. The Ca II H and K lines are also common in some kinds of → eruptive variable stars. These lines are not seen in → hot stars, and start to become visible in → A-type stars.

H and K, letters of alphabet, conventionally chosen; → line.

Any of the → spectral lines arising from → singly ionized helium in the atmosphere of → O-type and → Wolf-Rayet stars. He II lines are chiefly in absorption, but some of them, such as 4686 Å occur in emission in hotter stars. The presence of He II → absorption lines separates O types from → B-type stars. A number of these He II lines belong to the → Pickering series involving transitions with → principal quantum numbern = 4 and higher. Although the n = 3-4 (4686 Å) transition also belongs to ionized helium and often occurs in these hot stars, it does not belong to the Pickering series because it has a lower landing level quantum number (n = 3). The same goes for n = 2-5 (4026 Å).

→ helium; → line.

A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.

→ homogeneous; → linear; → differential; → equation.

An → emission or → absorption line in the spectra of various astronomical objects produced by the presence of hydrogen atoms in particular physical conditions.

→ hydrogen, → line.

Recognizing the lines in the spectrum of a star, nebula, galaxy, etc. using a calibration template.

→ identification; → line.

To deviate from the vertical or horizontal; slant.

Verbal form of → inclination.

The height of a spectral line above the continuum base.

→ intensity; → line.

In spectroscopy, same as → semi-forbidden line.

→ interconnection; → line.

An imaginary line following approximately the 180th meridian which, by international agreement in 1884, marks the beginning or or end of a day. The regions to the east of which are counted as being one day earlier in their calendar dates than the regions to the west.

→ international; → date; → line.

A spectral line formed in the interstellar medium, in particular an absorption line which does not participate in the periodic Doppler shift of intrinsic absorption lines in a binary star.

→ interstellar; → line.

In spectroscopy, same as → semi-forbidden line.

→ inter-; → system.

A line profile in which the emission is on the blue side of the absorption. It is usually interpreted as the redshift of the absorption component relative to emission lines, which necessitates infall of matter.

→ inverse; → P Cygni; → line; → profile.

→ lithium I line.

→ lithium; I for → neutral atom; → line.

1) A mark or stroke long in proportion to its breadth, made with a pen, pencil, or other tools.
2) Math.: A continuous extent of length, straight or curved, without breadth or thickness; the trace of a moving point.

M.E. li(g)ne "cord, rope, stroke, series," from O.E. line "rope, row of letters," partly from O.Fr. ligne, from L. linea "linen thread, string, line," from phrase linea restis "linen cord," from fem. of lineus (adj.) "of linen," from linum "flax, linen."

Xatt, xat, used also in Ar., but it has no Hebrew counterpart. Xat is probably of Iranian origin, from *kerš-/*xrah- "to draw, plow;" cf. Av. karš- "to draw; to plow," karša- "furrow;" Mid/Mod.Pers. kešidan, kašidan "to draw, protract, trail, drag, carry," dialectal Yaqnavi xaš "to draw," Qomi xaš "streak, stria, mark," Lori kerr "line;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base k^wels- "to plow."

In stellar atmosphere models, the effect of metallic lines on the atmospheric structure of stars. The additional opacities of thousands of metallic lines alter the radiative transfer, leading to changes in the temperature. The emergent spectrum is consequently modified.

→ line-blanketed model.