An Etymological Dictionary of Astronomy and Astrophysics
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A → forbidden line that is found in the spectra of → interstellar  → ionized gas. The nebular lines are emitted by several atomic species (e.g. O, O⁺, O⁺⁺, N⁺, S⁺⁺) and correspond to the → transition from the electronic → metastable state ¹D to the → ground state  ³P. Examples are the doubly ionized oxygen lines [O III] at 4959 and 5007 Å (→ [O III] doublet) and the ionized nitrogen doublet [N II] at 6548 and 6583 Å. See also → auroral line; → transauroral line.

→ nebular; → line.

In → iron meteorites, any of very fine parallel lines that cross each other at various angles. They can be seen after cutting diagonally across the sample.

Named after Johann G. Neumann, who discovered them in 1848 in the iron meteorite Braunau, which fell in 1847; → line.

The line connecting the ascending and descending nodes of an orbit.

→ nodal; → line.

A → linear differential equation if Q(x)≠ 0 on interval I.

→ nonhomogeneous; → linear; → differential; → equation.

Not a linear function of the relevant variables.
Containing a variable with an exponent other than one; opposite of → linear.

→ non-; → linear.

An electronic device whose output is not directly proportional to its input. For example, in a → diode the current is a nonlinear function of the voltage; its voltage-current characteristics do not obey → Ohm's law.

→ nonlinear; → device.

Same as → chaos.

→ nonlinear; → dynamics.

The instability of a physical or mathematical system that arises from the nonlinear nature of relevant variables and their interactions within the system.

→ nonlinear; → instability.

A system in which small changes can result in large effects, and large changes in small effects.

→ nonlinear; → system.

The property, condition, or state of being → nonlinear.

→ non-; → linearity.

Of computers, operating independently of, or disconnected from, an associated computer.

→ off; → line.

Emission or absorption lines on an electromagnetic spectrum generated by hydroxyl, → OH molecules. At present, four principal lines are known in the radio domain at frequencies of 1612, 1665, 1667, and 1720 MHz, or wavelengths of approximately 18 centimeters.

→ OH; → line.

The state when two or more devices are directly connected and are communicating efficiently.
Of computers, operating under the direct control of, or connected to, a main computer.

→ on; → line.

Preliminary reduction of observational data at a telescope simultaneously with their acquisition.

→ on-line; → reduction.

In the context of solar physics, a → magnetic field line when it crosses the solar surface only once, i.e., when it goes from surface to infinity. This is the case at a sufficiently large scale in → coronal holes. This is mostly not the case in → active regions.

→ open; → magnetic; → field; → line.

Perpendicular lines.

→ orthogonal; → line.

The path followed by an individual particle of fluid over an interval of time. It contrasts with the → streamline that represents an instantaneous picture of the motion of particles.

→ path; → line.

An ordinary spectral line emitted by atoms undergoing energy transitions that are allowed by the selection rules of quantum mechanics. → forbidden lines.

→ permitted; → line.

1) A long tubular conduit or series of pipes used to transport crude oil, natural gas, water, etc., often underground and over great distances.
2) A channel or process along which something passes or is provided at a steady rate.

→ pipe; → line.

A cord with a weight attached to one end, used to verify a true vertical alignment or to find the depth of water.

→ plumb; → line.

Šâqul, variants šâhul, sâhul, probably from sahi + suffix -ul, variant -âl. The first element sahi "upright, right," variants (Tabari, Torbat-Heydariyeyi: šax) "right, upright, straight, level," colloquial Pers. šaq (o raq = râst) "upright, erect." For the second element → -âl.