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

A dark disk seen in absorption against the bright nebular background. → proplyd.

From Fr. silhouette, in allusion to Étienne de Silhouette (1709-67), Fr. controller general of finances in 1759; perhaps from his ephemeral tenure; → disk.

Gerdé, → disk; siyah-rox, from siyah, → black, + rox, variant of ru(y) "face, surface; aspect; appearance," (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height").

A widely found mineral of silicon dioxide SiO₂, which is used as an ore of → silicon. It is a hard, white, or colorless crystalline compound with a high melting point, occurring abundantly as quartz, sand, flint, rock crystal, etc.

From L. silic- stem of → silex "hard stone, flint, boulder."

A common rock-forming → mineral belonging to a group formed from → silicon and → oxygen combined with various elements and classified by their crystalline structures. SiO₄ in the shape of a tetrahedron is the main component of the group. It has been estimated that about 95% of the Earth's crust is made up of silicate minerals. A salt of → silicic acid.

From → silica + → -ate.

1) Containing → silicon.
2) Of or pertaining to → silica or acids derived from it.

From silic-, from → silic + → -ic.

A general name for a family of chemical compounds containing the element silicon attached to oxide and hydroxyl groups.

→ silicic; → acid.

A non-metallic chemical element; symbol Si. Atomic number 14; atomic weight 28.0855; melting point 1,410°C; boiling point 2,355°C; specific gravity 2.33 at 25°C. It occurs in a combined state in minerals and rocks and constituting more than one fourth of the earth's crust.

From silic(a), from L. silex (genitive silicis) "flint, pebble" + -on, as in carbon and boron.

Silisiom, from Fr. silicium, from silic(a), as above, + -ium as in magnesium, barium.

The → nucleosynthetic process taking place in the interior of → massive stars whereby → silicon is transmuted into iron, nickel, and neighboring nuclei collectively called the → iron peak elements.

→ silicon; → burning.

The soft, lustrous fiber obtained as a filament from the cocoon of the silkworm (Dictionary.com).

M.E., from O.E. seolc, sioluc, from L. sericum "silk garment, silk," from neuter of sericus "silken," from Gk. serikos, from Seres, an eastern Asian people, probably the Chinese (cf. Chinese si "silk", Manchurian sirghe, Mongolian sirkek).

Abrišam "silk," from Mid.Pers. abrešom "silk," ultimately from Proto-Ir. *au-uris-, from *uris- "to turn, spin;" cf. rešté "thread, line, file," reštan, ristan, "to spin;" Mid.Pers. 'rws- "to turn to;" Av. uruuaēs- "to twist, turn."

The smoothing of primordial → density fluctuations at high frequencies caused by photon → diffusion. Before the → decoupling era, photons and → baryons were tightly coupled to each other by → Compton scattering. However, the transition to a transparent → Universe was not instantaneous. As the → opacity of the Universe dropped, the photons started diffusing away from the positions they had while opaque, hence undergoing a → random walk. Since the → acoustic waves in the decoupling era were driven by photon pressure, the photon diffusion also led to damping of the → baryon acoustic oscillations. Silk damping suppresses all perturbations with masses smaller than about 10¹³ Msun. The implication for a theory of → structure formation is that individual galaxies must have formed in a → top-down structure formation mechanism, i.e. by the fragmentation of larger objects. However, in theories of structure formation which include → non-baryonic dark matter galaxies can form from smaller objects in a → bottom-up scenario.

Joseph Silk (1942-); → damping.

A metallic → chemical element; symbol Ag (L. argentum). → Atomic number 47; → atomic weight 107.8682; → melting point 961.93°C; → boiling point 2,212°C; → specific gravity 10.5 at 20°C. Pure silver is nearly white, lustrous, soft, very ductile, malleable, and an excellent conductor of heat and electricity.
Silver is generated in stars through a special rapid process of → neutron captures. This process defers from the main → r-process, the main and weak → s-process, and charged particle freeze-outs. In other words, during a → supernova explosion, silver is formed in a different → fusion process from the one that forms → gold (Hansen et al., 2012, A&A 545, A31).

M.E. silver(e), selver(e), selfer; O.E. seolfor "silver;" cf. O.S. silvbar, O.N. silfr, M.Du. silver, Du. zilver, O.H.G. sillabar, Ger. silber, Goth. silubr, akin to Serbo-Croatian srebro, Rus. serebo, Lith. sidabras "silver."
L. argentum "silver, white money," from PIE *arg-ent-, from PIE *arg- "to be bright, shine;" cf. Av. ərəzata- "silver," auruša- "white" (Mid.Pers. arus "white, bright"); O.Pers. ardata- "silver;" Mod.Pers. arziz "silvery metal tin;" Skt. arjuna- "white, shining," rajata- "silver;" Gk. argos "white," arguron "silver;" Arm. arcat; Hittite harki- "white."

Noqré from Sogdian nâkartak "uncoined (silver)," literally "undone," from nâ- negation prefix "not, no" (Mid.Pers. ne, O.Pers. naiy, Av. na-, (particle of negation noit), Skt. na-, (ned), Gk. né- "not," L. ne-, in-, un-, PIE *ne-) + kartak "done," p.p. of kardan "to do, to make;" kâr "work," variant kar (Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build;" Av. kərənaoiti "he makes;" cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base k^wer- "to do, to make"), Sogdian nâktênê "of silver." Note that another word in Pers. for silver is sim, which has a semantic form comparable to that of noqré, since it derives from Mid.Pers. asêm, from Gk. asemon "without mark, uncoined, shapeless, formless," from argurion asemon "uncoined money."

A large on-line astronomical database, developed at the Centre de Données astronomiques de Strasbourg, → CDS in France. It provides a large collection of astronomical data, including cross-identifications, bibliography, and measurements for astronomical objects outside the solar system.

SIMBAD, short for Set of Identifications, Measurements, and Bibliography for Astronomical Data.

1) Geometry: Having the same shape; representing the same figure drawn to different scales (same corresponding angles and proportional sides).
2) Math.: Related by means of a → similarity transformation.

From Fr. similaire, from L. similis "like," → simulate.

Hamânand, contraction of hammânand, from ham-, → com-, + mânand "resembling, like," → simulate.

Two → square matrices A and B that are related by B = X^-1AX, where X is a square → nonsingular matrix.

→ similar; → matrix.

Polygons that are exactly the same shape, but can be different sizes.

→ similar; → polygon.

The state of being similar; likeness; resemblance.

→ similar; → -ity.

1) A transformation that preserves angles and changes all distances in the same ratio.
2) A transformation of the form B = X^-1AX relating two → square matrices A and B.

→ similarity; → transformation.

1) Chem.: Composed of only one → substance or → element.
2) Math.: Consisting of, involving, or describable by → terms of the → first degree.
3) Music: Uncompounded or without overtones.

M.E., from O.Fr. simple, from L. simplus "simple, single," variant of simplex, from PIE root *sem- "one, together;" cf. Pers. ham "together," → com-, Skt. sam "together;" + *plac- "-fold," from PIE *plek- "to plait," → multiply.

Sâdé "simple, unmixed, smooth, erased, plain;" cf. Khotanese sāta- "smooth;" Baluchi sāt/sāy-, sāh- "to shave;" Av. si-, sā- "to sharpen, cut;" Skt. śā- "to sharpen, whet" (Cheung 2007); see also → precise.

Statistics: An event consisting of a single point of the → sample space.

→ simple; → event.

A fraction in which the → numerator and → denominator are positive → integer numbers. Compare → compound fraction.

→ simple; → fraction.

The motion of a body subjected to a restraining force which is directly proportional to the displacement from a fixed point in the line of motion. The equation of simple harmonic motion is given by x = A sin(ωt + θ₀), where x is the body's displacement from equilibrium position, A is the → amplitude, or the magnitude of harmonic oscillations, ω is the → angular frequency, t is the time elapsed, and θ₀ is the → initial phase angle.

→ simple; → harmonic; → motion.