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

The highest correlation between linear functions of two data sets when specific restrictions are imposed upon them.

→ canonical; → correlation.

The process in which an atomic, nuclear, or astronomical system acquires an additional particle or body.

From M.Fr. capture "a taking," from L. captura "a taking," from captus p.p. of capere "to take, hold, seize;" PIE base *kap- "to grasp" (cf. Skt. kapati "measure equal to the capacity of the hollows of the two hands joined;" Gk. kaptein "to swallow;" O.Ir. cacht "servant-girl," literally "captive;" Goth. haban "have, hold;" O.E. habban, E. have "to have, hold;" probably Mod.Pers. qâp-, qâpidan, kapidan "to seize, rob").

Gir-oft, composite verb from gir + oft. Gir "take, seize, hold," from gereftan, from O.Pers./Av. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha- "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE *ghrebh- "to seize." Oft, from oftâtan "to fall; to befal, happen," Mid.Pers. opastan, Av. pat- " to fly, fall, rush," Skt. patati "he flies, falls," L. petere "to fall, rush out," Gk. piptein "to fall," PIE base *pet- "to fly, to rush." Gir-andâzi, from gir + andâzi, verbal noun from gir-andâxtan "to throw, cast; to do, make."

One of the first scientific hypotheses about the formation of the Moon, according to which the Moon formed elsewhere in the solar system and was pulled into a stable orbit by Earth's gravity. Observational facts do not confirm this hypothesis. For example, analysis of rocks from the Apollo landings confirm the Moon is made of similar material and rock as the Earth from about the same time and have almost identical oxygen isotopes in them. Moreover, a captured moon, like Mars' → Phobos and → Deimos do not have a spherical shape. See also → giant impact hypothesis, → fission theory, → co-formation theory.

→ capture; → theory.

Any of the four principal directions or points of the compass, → north, → east, → south, and → west. See also: → cardinal point.

→ cardinal; → direction.

1a) A state of mind in which one is troubled; worry, anxiety, or concern; a cause or object of worry, anxiety, concern, etc.
1b) Serious attention; solicitude; heed; caution.
2a) To be concerned or solicitous; have thought or regard.
2b) To be concerned or have a special preference (Dictionary.com).

M.E., from O.E. caru, cearu "sorrow, anxiety, grief," cognate with Gothic kara, O.H.G. chara lament; M.En. caren, O.E. cearian, carian "be anxious, grieve."

Timâr "care, attendance on the sick; custody; sorrow;" Mid.Pers. têmâr "care; grief"

1) Cautious in one's actions.
2) Taking pains in one's work; exact; thorough.
3) (of things) Done or performed with accuracy or caution (Dictionary.com).

→ care; + -ful, a suffix meaning "characterized by; full of; able to;" → full.

If f(x) and φ(x) are two → continuous functions on the → interval [a,b] and → differentiable within it, and φ'(x) does not vanish anywhere inside the interval, there will be found, in [a,b], some point x = c, such that [f(b) - f(a)] / [φ(b) - φ(a)] = f'(c) / φ'(c).

→ Cauchy's equation; → theorem.

In → special relativity, the causal relationship between → events involving a → light cone.

→ causal; → structure.

An often temporary cessation of hostilities during wartime for a specific purpose. It may be unilateral or bilateral.

From cease from O.Fr. cesser "to come to an end, stop," from L. cessare "to cease, go slow, be idle," + → fire.

Âtašbas, from âtaš, → fire, + bas, from bas kardan "to stop, end; leave."

An imaginary sphere, of large but indefinite dimension, used as a basis to define the position coordinates of celestial bodies. The center can be the Earth, the observer, or any other point which plays the role of origin for a given system of coordinates. Seen from the Earth, the celestial sphere rotates around the → celestial axis every 23h 56m 04s (the → sidereal day), as a result of the Earth's rotation. Two important circles on the celestial sphere are the → celestial equator and the → ecliptic. The angle between them, about 23.40 degrees, is known as the → obliquity of the ecliptic. The celestial equator and the ecliptic intersect at two points, → vernal equinox and → autumnal equinox. The positions of the → celestial poles and therefore that of the → celestial equator move gradually on the celestial sphere, due to → precession.

→ celestial; → sphere.

A statement about the characteristics of the sampling distribution of means of → random samples from a given → statistical population. For any set of independent, identically distributed random variables, X₁, X₂,..., X_n, with a → mean μ and → variance σ², the distribution of the means is equal to the mean of the population from which the samples were drawn. Moreover, if the original population has a → normal distribution, the sampling distribution of means will also be normal. If the original population is not normally distributed, the sampling distribution of means will increasingly approximate a normal distribution as sample size increases.

→ central; → limit; → theorem.

Once qualified as the largest known → asteroid, Ceres is now classified as a → dwarf planet (2006 IAU General Assembly). It is approximately 950 km across, and resides with tens of thousands of asteroids in the main → asteroid belt; it is the largest body of the belt. Its mass is 9.4 × 10²⁰ kg, its → rotation period 9.074 hours, its → orbital period 4.60 years, and its → semi-major axis 2.767 AU. NASA's → Dawn spacecraft, which was placed in orbit around Ceres in 2015, has mapped its surface in great detail from a distance. Dawn caught sight of bright spots that soon resolved into more than 130 bright patches, most of them tied to craters. The most prominent of these spots lie inside the crater → Occator. The patches turned out to be carbonate salts, which only form in the presence of water. Since water skips to gas almost immediately on the dwarf planet's surface, the discovery of carbonates suggested that there was liquid beneath the dwarf planet's crust. Aside from craters, the only outstanding feature On Ceres is a single mountain, Ahuna Mons. It formed about 250 million years ago when plumes of saltwater and mud rose and erupted from within Ceres.

Ceres in Roman mythology was the goddess of growing plants and of motherly love. She was equivalent to Demeter in Gk. mythology.

A succession of → nuclear fissions when the neutrons released by previous fissions produce other nuclear fissions which themselves cause other reactions and the reactions goes on increasing exponentially.

→ chain; → reaction.

A → change or → transformation in which a → substance → decomposes, → combines with other → substances, or interchanges constituents with other substances.

→ chemical; → reaction.

Visible radiation emitted when → charged particles pass through a transparent medium faster than the speed of light in that medium.

Named after Pavel A. Čerenkov (1904-1990), Russian physicist, who discovered the phenomenon. He shared the Nobel prize 1958 in physics with Ilya Frank and Igor Tamm, who in 1937 gave the theoretical explanation for this radiation.

A probability density function, denoted χ², that gives the distribution of the sum of squares of k independent random variables, each being drawn from the normal distribution with zero mean and unit variance. The integer k is the number of degrees of freedom. The distribution has a positive skew; the skew is less with more degrees of freedom. As degrees of freedom increase, the chi-square distribution approaches a normal distribution. The most common application is chi-square tests for goodness of fit of an observed distribution to a theoretical one. If χ² = 0 the agreement is perfect.

Chi Gk. letter of alphabet; → square; → distribution.

Vâbâžeš, → distribution; do, → two.

A region of the stellar atmosphere situated above its → photosphere. The Sun's chromosphere extends from the about 500 km above the photosphere basis, up to 9,000 km, where it meets the → corona. For a plane-parallel model, the chromosphere is more or less continuous throughout the first 1,500 km, but breaks into indented spicules beyond that height. The chromosphere temperature grows from 4,400 K at 500 km to almost 6,000 K at 1,000-2,000 km. A rapid growth of coronal temperatures is registered at heights of about 2,500 km (the transition region), the exact height depending on the local magnetic field intensity. Actually, the chromosphere is made of rising and, often, falling jets called → spicules, which go up to 15,000 km. In the uppermost part of the chromosphere the density is the millionth part of its density at the base. Immediately before or after a solar → total eclipse, the chromosphere becomes visible either as a crescent or as a red → diamond ring, due to → H-alpha emission, from which it also gets its name. Moreover, the chromosphere can be seen in → H and K lines of calcium during eclipses, and in ultraviolet emission lines from space. The presence of the chromosphere around cold → dwarf stars is deduced from similar emissions (M.S.: SDE).

→ chromo- "color," because of the reddish-pink color of the chromosphere which is seen around the Sun during a total eclipse and is due to the dominance of the → H-alpha line; → sphere.

1) The boundary line of a circle.
2) The boundary line of a figure, area, or object.

From M.E., from O.Fr. circonference, from L. circumferentia, from circumferens, circumferent-, pr.p. of circumferre "to carry around," from → circum- + ferre "to carry," from PIE root *bher-; "to carry;" cf. Av./O.Pers. bar- "to bear, carry," barəθre "to bear (infinitive)," barəθri- "a female that bears (children), a mother," Mod.Pers. bordan "to carry," Skt. bharati "he carries," Gk. pherein, P.Gmc. *beranan (O.H.G. beran, Goth. bairan "to carry").

Pirâmun, from Mid.Pers. pêrâmôn, from O.Pers./Av. mâ-, mây- "to measure," from PIE *me- "measure," cf. Skt. mati "measures," matra "measure," Gk. metra "lot, portion," L. metri "to measure." In Mod.Pers. this stem is extant in peymaân, peymaâné, âzmun, âzmâyeš.

A sphere containing a polyhedron (such as a pyramid) all of whose vertices lie on the surface of the sphere. The polyhedron so contained is said to be inscribed in the sphere.

Circumscribed p.p. of → circumscribe; → sphere.

Math.: The property of a set in which the application of a given mathematical operation to any member of the set always has another member of the set as its result.
The intersection of all closed sets that contain a given set.

M.E., from M.Fr., from O.Fr. closure "that which encloses," from L. clausura "lock, fortress, a closing," from p.p. stem of claudere "to close."

Bandeš, verbal noun of bastan "to shut, bind; to clot; to form seed buds," from Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie;" Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind," cf. Ger. binden, E. bind.