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

A numerical method for modeling → compressible hydrodynamic flows, which uses particles to simulate a continuous fluid flow. Because the system of hydrodynamical basic equations can be analytically solved only for few exceptional cases, the SPH method provides a numerical algorithm to solve systems of coupled → partial differential equations for continuous field quantities. The main advantage of the method is that it does not require a computational grid to calculate spatial → derivatives and that it is a Lagrangian method, which automatically focuses attention on fluid elements. The equations of motion and continuity are expressed in terms of ordinary differential equations where the body forces become classical forces between particles. This method was first independently developed by Lucy (1977, AJ 82, 1013) and Gingold & Monaghan (1977, MNRAS 181, 375).

Smoothed Particle Hydrodynamics, first used by Gingold & Monaghan (1977); → smooth; → particle; → hydrodynamics.

The branch of astrophysics concerned with the study of the physical properties of the Sun based on the most detailed observations which can be obtained for a star.

→ solar; → physics.

The branch of condensed matter physics concerned with the study of rigid matter or solids in terms of their constituent particles (electrons and nuclei). The bulk of solid-state physics theory and research is focused on the electromagnetic, thermodynamic, and structural properties of crystalline solids.

→ solid state; → physics.

A new area of science and technology which exploits the intrinsic → spin of electrons and its associated → magnetic moment, in addition to its fundamental electronic charge, in solid-state devices. In brief, spin-based electronics. For example, information could be transported or stored through the spin-up or spin-down states of electrons. Spintronics techniques are capable of much higher speed while requiring less power than the conventional method of using electron charges to represent data. The first use of spintronics was in the late 1980s with the development of → giant magnetoresistance (GMR) read heads for disk drives

Short for → spin + → electronics.

The theory developed since the 1970s, which is based on the theories and discoveries since the 1930s, and aims at explaining the fundamental structure of matter. According to the standard model, everything in the universe is made from a few basic building blocks called fundamental particles, governed by four fundamental forces. The particles occur in two basic types, called quarks and leptons. Three of the four fundamental forces (except gravity) and their carrier particles are included in the Standard Model. The Standard Model has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Over time and through many experiments, the Standard Model has become established as a well-tested physics theory.

→ standard; → model; → particle; → physics.

The branch of → mechanics which studies the laws of composition of forces and the conditions of equilibrium of material bodies under the action of forces.

→ static; → -ics.

Istâyik, from istâ, → static + -ik, → -ics.

→ statistical physics.

→ statistical; → mechanics.

The branch of physics that applies methods of → probability theory and → statistics to the behavior of large numbers of microscopic particles (such as molecules, atoms, or subatomic particles) in order to explain and predict the overall properties of the system composed of such particles.

→ statistical; → physics.

Same as → statistical mechanics.

→ statistical; → thermodynamics.

A branch of applied mathematics that deals with the collection and interpretation of quantitative data and the use of probability theory to estimate population parameters.

From Ger. Statistik "political science," from Mod.L. statisticus (collegium) "state affairs," from It. statista "person skilled in statecraft," from stato "state," ultimately from L. status "position, form of government;" cognate with Pers. ist-, istâdan "to stand" (Mid.Pers. êstâtan; O.Pers./Av. sta- "to stand, stand still; set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to stand").

Âmâr "computation, arithmetic; statistics," from âmârdan "to reckon, to calculate," related to ošmârdan, šomârdan, šomordan "to count, to calculate," mar, mâr- "count, reckon, measure," bimar "countless," nahmâr "great, large, big;" Mid.Pers. âmâr "calculating, reckoning;" Av. base mar- "to have in mind, remember, recall," hišmar-; cf. Skt. smr-, smarati "to remember, he remembers," L. memor, memoria, Gk. mermera "care," martyr "witness."

The field of → astrophysics concerned with the study of the physical characteristics of stars, more specifically their → internal structure, physical processes taking place in their interiors, atmospheres, → stellar winds, → mass loss, interaction with the → interstellar medium, as well as the physical laws governing → star formation. Same as → stellar physics and → stellar astronomy.

→ stellar; → astrophysics.

The field of astrophysics that describes systems of many → point mass particles whose mutual gravitational interactions determine their orbits. Theses systems include → star clusters, → globular clusters, and galaxies (→ galaxy) consisting of about 10²-10³, 10⁴-10⁶, and up to about 10¹² members respectively. Stellar dynamics deals with systems in which each member contributes importantly to the overall gravitational field and is usually concerned with the statistical properties of many orbits. It can be compared to the → kinetic theory of gases developed in the late 19th century. In contrast, → celestial mechanics deals with systems where the gravitational force of a massive planet or star determines the orbits of its satellites.

→ stellar; → dynamics.

Same as → stellar astrophysics.

→ stellar; → physics.

The study of the grammatical relationships among signs, independently of their meaning (→ semantics. See also → syntax.

→ syntax; → -ics.

Biology: The science that deals with the systematic naming and classification of all kinds of organisms.

From → systematic + → -ics.

The science or art of assembling, shaping, or ornamenting materials in construction; the constructive arts in general. → plate tectonics

L.L. tectonicus, from Gk. tektonikos "pertaining to building," from tekton (genitive tektonos) "builder, carpenter," → technique.

Sâzânik, from sâzân pr.p. of sâz-, sâxtan "to build, make, fashion; to adapt, adjust, be fit" (Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach") + -ik, → -ics.

A body of topics for study or discussion.

From L. themat-, from thema, → theme, + → -ics.

An astrophysical study or research group mainly concerned with theory rather than observation.

→ theoretical; → astrophysics.

A branch of physics concerned with the relations between heat and other forms of energy and how these affect temperature, pressure, volume, mechanical action, and work.

→ thermo-; → dynamics, coined by the Scottish physicist William Thomson (Lord Kelvin, 1824-1907), in 1849.

The → entropy of an idealized state of maximum order is zero at the temperature of → absolute zero. Another version of this law: As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.

→ third; → law; → thermodynamics.