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

The ability to connect to a computer from a remote location and to control the machine once the connection has been made.

→ remote; → access.

1) Control of the operation or performance of an apparatus from a distance, as the control of a guided missile by radio signals.
2) A device used to control the operation of an apparatus or machine, as a television set, from a distance.

→ remote; → control.

A mode of astronomical observation in which the observer is situated in a remote place from the telescope. The data are collected through assistants in contact with the telescope, and are transmitted along some communication pathway for local processing and interpretation.

→ remote; observing, verbal noun of → observe.

Technique that utilizes electromagnetic waves to detect, measure, and obtain information about an object that is not in contact with the sensing apparatus.

→ remote; → sense.

Hesgari, noun from hesgar, → sensor; dur, → remote.

The theorem stating that the value of the line integral of a complex function, taken along a simple closed curve encircling a finite number of isolated singularities, is given by 2πi times the sum of the residues of the function at each of the singularities.

→ residue; → theorem.

The first successful measurement of the → speed of light carried out by the Danish astronomer Ole Rømer in 1675 at Paris Observatory. Astronomers knew that the mean period of revolution for Jupiter's innermost satellite → Io (Jupiter I) was 42.5 hours. During this period Io was sometimes eclipsed by Jupiter. Astronomers expected that if Io was visible at some time it must be visible 42.5 hours later. But Ole Rømer discovered that there were many irregularities in Io's orbital period. Sometimes Io appeared too early and other times too late in relation to the expected times. The irregularities repeated themselves precisely at a one-year interval, which meant that they must be connected to the Earth's rotation around the Sun. Rømer attributed this difference in time to the additional distance the light from Io had to travel at different times, and used this information to calculate the speed of light. He found that it takes light 22 minutes to traverse the Earth's orbital diameter; the correct figure was later determined to be 16 minutes and 40 seconds. Rømer was able to measure the speed of light to be 230,000 km s^-1. Although this figure was very close to the currently accepted value of 300,000 km s^-1, it was rejected by the scientific community of the time, who assumed it to be much too high a figure.

Ole Rømer (1664-1710); → measurement.

If a function f(x) is → continuous on an interval [a,b] and is → differentiable at all points within this interval, and vanishes at the end points x = a and x = b, that is f(a) = f(b) = 0, then inside [a,b] there exists at least one point x = c, a < c < b, at which the derivative f'(x) vanishes.

Named after Michel Rolle (1652-1719), a French mathematician; → theorem.

A uniqueness theorem involving the equations of state of stellar structure. → Vogt-Russell theorem.

Named after the German astronomer Heinrich Vogt (1890-1968) and the American astronomer Henry Norris Russell (1877-1957); → theorem.

Same as → Nyquist-Shannon sampling theorem.

→ sampling; → theorem.

Same as → sampling theorem.

→ Shannon entropy; → sampling; → theorem.

The → moment of inertia of a body about an arbitrary axis x' is equal to the sum of its moment of inertia about axis x, passing through the center of mass of the body and parallel to axis x', and the product of the mass M of the body by the square of the distance d between axes x and x': I_x' = I_x + Md². Same as → parallel axis theorem.

Named after Jakop Steiner (1796-1863), a Swiss mathematician who derived this statement; → theorem.

The body of expanding gas ejected at a speed of about 10,000 km s^-1 by a → supernova explosion, observed as a diffuse → gaseous nebula, often with a → shell-like structure. Supernova remnants are generally powerful → radio sources. The evolution of the SNR can be divided into different phases according to the dominant physical processes. Simplified models are made for the first stages, to get an idea of typical time scales, expansion velocities, and sizes. The three main phases are: 1) the → free expansion phase, 2) the → Sedov-Taylor phase, and 3) the → snowplow phase.

→ supernova; → remnant.

1) Highest in rank or authority.
2) Of the highest quality, degree, character, importance, etc.

M.E., from M.Fr. suprême, and directly from L. supremus "highest," superlative of superus "situated above," from super "above," → super-.

Abartom "highest," from abar "high, upon," → super-, + -tom superlative suffix, → extreme.

In a rapidly rotating fluid, the fluid velocity is constant along any line parallel to the axis of rotation.

→ Taylor number; Joseph Proudman (1888-1975), British mathematician and oceanographer.

A → proposition, → statement, or → formula in → mathematics or → logic deduced from → axioms, other propositions, → assumptions, → premises, or formulas. Theorems are statements which can be proved. For example, → Fourier theorem; → Liouville's theorem; → Woltjer's theorem.

From M.Fr. théorème, from L.L. theorema, from Gk. theorema "spectacle, speculation," in Euclid "proposition to be proved," from theorein "to look at, speculate, consider."

Farbin, from far- intensive prefix "much, abundant; elegantly; forward" (Mid.Pers. fra- "forward, before; much; around;" O.Pers. fra- "forward, forth;" Av. frā, fərā-, fra- "forward, forth; excessive;" cf. Skt. prá- "before; forward, in front;" Gk. pro "before, in front of;" L. pro "on behalf of, in place of, before, for;" PIE *pro-) + bin, present stem of didan "to see," from Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" cf. Skt. veda "I know;" Gk. oida "I know," idein "to see;" L. videre "to see;" PIE base *weid- "to know, to see."

The emission of electromagnetic radiation from high temperature plasma, produced as electrons are deviated by positive ions. Same as → free-free emission

→ thermal; → bremsstrahlung.

1) Physics: A → potential that satisfies both → Poisson's equation and the → boundary conditions pertinent to a particular field is the only possible potential.
2) Math.: If two → continuous functions φ(t) and ψ(t) have one and the same → Laplace transform F(p), then these functions are identically equal.
3) Astro.: A → black hole can only be characterized by its → mass, → electric charge, and → angular momentum. See also → no hair theorem.

→ uniqueness; → theorem.

In → Young's experiment of → interference with double apertures, if a monochromatic source is a considerable distance from the → aperture plane and aperture separation is small, → fringe visibility from an extended source is proportional to the → Fourier transform of the source's spatial distribution. The transform variable is the angular separation of the aperture-plane sampling points divided by the wavelength. The van Cittert-Zernike Theorem is at the heart of → aperture synthesis.

Developed independently by Dutch physicists Pieter Hendrick van Cittert (1889-1959) in 1934 and Frits Zernike (1888-1966) in 1939; → theorem.

The → moment of the resultant of a → coplanar system of → concurrent forces about any center is equal to the algebraic sum of the moments of the component forces about that center.

Named after Pierre Varignon (1654-1722), a French mathematician, who outlined the fundamentals of statics in his book Projet d'une nouvelle mécanique (1687).

A → supernova remnant located in the southern Milky Way in the constellation → Vela. It has a large angular diameter of about 8° and lies 250 ± 30 pc away (Cha et al. 1999, ApJ 515, L25). Its overall emission is dominated by the interaction of the → supernova blast wave with the → interstellar medium. This SNR is also notable for a number of protrusions extending well beyond its rim, which were suggested to be fragments of ejecta from the supernova explosion. X-ray spectroscopy has since confirmed several of these protrusions to indeed be strongly enriched with ejecta. The age of the SNR is estimated to be ~11,000 years, based on the spin-down rate of the associated → Vela pulsar, but ages as large as 20,000-30,000 years have also been argued.

→ Vela; → supernova remnant.