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

In classical mechanics, an analytical method applied to a material sphere to determine the gravitational field at a point outside or inside the sphere. Newton's shell theorem states that: 1) The gravitational field outside a uniform spherical shell (i.e. a hollow ball) is the same as if the entire mass of the shell is concentrated at the center of the sphere. 2) The gravitational field inside the spherical shell is zero, regardless of the location within the shell. 3) Inside a solid sphere of constant density, the gravitational force varies linearly with distance from the center, being zero at the center of mass. For the relativistic generalization of this theorem, see → Birkhoff's theorem.

→ Newton; → shell; → theorem.

There are only three parameters that can be applied by an outside observer relating to a → black hole: → mass, → electric charge, and → angular momentum. The collapse of a star into a black hole wipes out all other details of its structure, and the observer can never discover any other properties of the star which formed the black hole. In other words, none of its characteristics leave any trace outside the black hole, and that is what is meant by "hair."

No, M.E., from O.E. na "never, no," cognate with Pers. na, nâ, → non-; → hair; → theorem.

Farbin, → theorem; bimuyi, noun from bimu "without hair," from bi- "without" (→ in-) + mu, → hair.
Kacali "baldness," from kacal "bald," also "crooked, bandy-legged," from kajal, from kaj "crooked, curved, bent" + → -al; probably unrelated to kal "bald," → colure.

A → symmetry in a physical system leads to a → conserved quantity. For example, symmetry under → translation corresponds to conservation of → momentum, symmetry under → rotation to conservation of → angular momentum, and symmetry in → time to conservation of → energy. The Noether symmetry theorem is a fundamental tool of modern theoretical physics and the calculus of variations, allowing to derive conserved quantities from the existence of variational symmetries.

Named in honor of the German-American woman mathematician Amalie Emmy Noether (1182-1935), who published the theorem in 1918 ("Invariante Variationsprobleme," Nachr. D. König. Gesellsch. D. Wiss. Zu Göttingen, Math-phys. Klasse 1918: 235-257).

The minimum number of resolution elements required to properly sample a signal, such as a star image, without causing erroneous effects known as aliasing. For electronic imaging, this number is generally taken as 2 pixels across the seeing disk diameter at the half intensity points. Also called → Shannon's sampling theorem and → sampling theorem.

Named after Harry Nyquist (1889-1976), a Swedish-born American physicist, who made important contributions to information theory, and Claude Elwood Shannon (1916-2001), an American mathematician and pioneer of information theory; → theorem.

The → moment of inertia of a body about any given axis is the moment of inertia about a parallel axis through the center of mass, plus the moment of inertia about the given axis if the mass were located at the center of mass. same as → Steiner's theorem.

→ parallel; → axis; → theorem.

A theorem relating the → Fourier coefficients to the function that they describe. It states that: (1/L) ∫ |f(x)|²dx (integrated from x₀ to x₀ + L) = (a₀/2)² + (1/2) Σ (a_r² + b_r²) (summed from r = 1 to ∞). In other words, the sum of the moduli squared of the complex Fourier coefficients is equal to the average value of |f(x)|² over one period.

Named after Marc-Antoine Parseval (1755-1836), French mathematician; → theorem.

A collapsing object whose radius is less than its Schwarzschild radius must collapse into a singularity.

→ Penrose process; → theorem.

The → moment of inertia of a plane object (→ lamina) about an axis perpendicular to the plane is equal to the sum of the moments of inertia about any two perpendicular axes in the plane. Thus if x and y axes are in the plane, I_z = I_x + I_y.

→ perpendicular; → axis; → theorem.

In an → isolated system, any initial state will occur again in the course of the → evolution of the system over a sufficiently long but finite → time.

→ Poincaré sphere; → recurrence; → theorem.

The space through which electromagnetic radiation passes is filled with electric and magnetic fields at right angles to each other and to the direction of propagation of the radiation. The rate of energy transfer is given by the Poynting vector.

In honor of John Henry Poynting (1852-1914), English physicist; → theorem.

Logic: An initial → proposition or statement that is known or assumed to be → true and on which a logical → argument is based.

From M.E. premiss, from O.Fr. premisse, from M.L. premissa (propositio) "(the proposition) set before," feminine p.p. of L. praemittere "send or put before," from prae "before," → pre-, + mittere "to send," → mission.

Pišpâyé, from piš-, → pre-, + pâyé, → base.

The proposition that the → square of the → hypotenuse of a → right triangle is equal to the → sum of the squares of the other two sides: a² + b² = c².

After Pythagoras (c570 BC-c495BC), Greek philosopher and mathematician; → theorem.

1) General: Any theorem that expresses various reciprocal relations for the behavior of some physical systems, in which input and output can be interchanged without altering the response of the system to a given excitation.
2) In classical electromagnetism, the theorem stating that the current in a detector divided by the voltage at the source remains constant when source and detector are interchanged, as long as the frequency and all the impedances are left unchanged.

Reciprocity, from L. reciproc(us) "returning the same way, alternating" + → -ity; → theorem.

Farbin, → theorem; dosuyegi, quality noun of dosuyé nuanced term of dosu "two-sided," from do, → two, + su "direction, side," from Mid.Pers. sôk "direction, side."

A unit used for measuring the effective dose of radiation received by a living organism. It is the quantity of radiation whose biological effect is equal to that produced by one → roentgen of → X-rays. 1 rem = 0.01 sievert (Sv) or 10 → millisieverts.

Rem, acronym for roentgen equivalent man. The unit was introduced in 1944 by Herbert M. Parker (1910-1984), a radiation physicist and co-inventor of the Paterson-Parker Radium Therapy System.

1) To continue in the same state.
2) To stay behind or in the same place.

M.E. remainen, from O.Fr. remain-, stressed stem of remanoir "to stay, dwell, remain," from L. remanere "to remain, to stay behind; be left behind," from → re- "back" + manere "to stay, remain" (from PIE root *men- "to remain," cf. Pers. mân-, mândan, as below.

Mândan "to remain, stay" (mân "house, home;" Mid.Pers. mândan "to remain, stay;" O.Pers. mān- "to remain, dwell;" Av. man- "to remain, dwell; to wait;" Gk. menein "to remain;" L. manere "to stay, abide" (Fr. maison, ménage; E. manor, mansion, permanent); PIE base *men- "to remain, wait for."

An effect that remains in a system for a while after the physical cause has been removed. For example the light remaining in a detector after elimination of the source, or the magnetic induction that remains in a material after removal of the magnetizing field.

From reman(ent), → remanent + -ence a noun suffix.

Noun of → pasmân.

Possessing → remanence.

M.E. from L. remanent- (stem of remanens), pr.p. of remanere "to remain, stay behind," from → re- "back" + manere "to stay, remain," cognate with Pers. mândan "to stay, remain," as below.

Pasmân, from pas- "behind," variant pošt "back; the back; behind" (Mid.Pers. pas "behind, before, after;" O.Pers. pasā "after;" Av. pasca "behind (of space); then, afterward (of time);" cf. Skt. paścā "behind, after, later;" L. post, as above; O.C.S. po "behind, after;" Lith. pas "at, by;" PIE *pos-, *posko-) + mân present stem of mândan "to remain, stay" (mân "house, home;" Mid.Pers. mândan "to remain, stay;" O.Pers. mān- "to remain, dwell;" Av. man- "to remain, dwell; to wait;" Gk. menein "to remain;" L. manere "to stay, abide" (Fr. maison, ménage; E. manor, mansion, permanent); PIE base *men- "to remain, wait for").

Something that cures or relieves a disease or bodily disorder; a healing medicine, application, or treatment (Dictionary.com).

M.E. remedie, O.Fr. remede "remedy, cure" and directly from L. remedium "a cure, remedy, medicine, antidote," from → re-, + mederi "to heal."

Darmân, Mid.Pers. darmân "remedy, medicine," related to O.Pers. duruva- "firm, certain, immune;" Av. druua- "healthy;" cf. Skt. dhruva- "fixed, firm;" related to Mid.Pers. drôd (Pers. dorud) "thriving," durust (Pers. dorost) "whole, right, healthy," Baloci durâh "healthy, whole;" Khotanese drunna- "healthy," → integral.

A usually small part of something that is left after the rest of it has been used, removed, or destroyed. → supernova remnant.

M.E., from O.Fr. remnant, pr.p. of remenoir "to remain," from L. remanere "to remain, stay behind," from → re- "back" + manere "to stay, remain," cognate with Pers. mândan "to stay, remain," as below.

Bâzmândé "remnant," from bâz-, → re-, + mândé p.p. of mândan "to remain, stay" (mân "house, home;" Mid.Pers. mândan "to remain, stay;" O.Pers. mān- "to remain, dwell;" Av. man- "to remain, dwell; to wait;" Gk. menein "to remain;" L. manere "to stay, abide" (Fr. maison, ménage; E. manor, mansion, permanent); PIE base *men- "to remain, wait for").

Situated at some distance away.

M.E. from L. remotus "afar off, remote," p.p. of removere "move back or away," from → re- "back, away" + movere "to move."

Dur, from Mid.Pers. dūr "far, distant, remote;" O.Pers. dūra- "far (in time or space)," dūraiy "afar, far away, far and wide;" Av. dūra-, dūirē "far," from dav- "to move away;" cf. Skt. dūrá- "far; distance (in space and time);" PIE base *deu- "to move forward, pass;" cf. Gk. den "for a long time," deros "lasting long."