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

A ring-like structure of swept-up → gas and → dust around a → supernova remnant. See also: → free expansion phase, → Sedov-Taylor phase, → snowplow phase.

→ supernova remnant (SNR); → shell.

A method allowing for a simplified solution to the → radiative transfer equation at frequencies of spectral lines in media moving with a high velocity gradient. This method assumes that the macroscopic velocity gradients are more important than local random variations of thermal line width: dv/dr > v_th/l, where dv/dr is the velocity gradient, v_th is the thermal broadening of the line, and l the length scale. The Sobolev approximation is only valid if the conditions of the gas do not change over the → Sobolev length. Under the Sobolev approximation, each point in the medium is isolated from other points, and the → radiative transfer problem becomes a local one and therefore much easier to solve.

Named after the Russian astronomer Viktor Viktorovich Sobolev, Moving Envelopes of Stars [in Russian], Leningr. Gos. Univ., Leningrad (1947) [translated by S. Gaposchkin, Harvard Univ. Press, Cambridge, Mass. (1960)]; → approximation.

In the → Sobolev approximation, the length over which the conditions of the gas do not change and the approximation is valid. It is expressed by: l_s = v_th/(dv/dr), where v_th is the thermal line width and (dv/dr) the velocity gradient. In other words, the length over which the profile function of a line is shifted through a distance equal to its own width by the macroscopic velocity gradients that exist in the moving medium.

→ Sobolev approximation; → length.

Of or pertaining to human society.

→ society; → -al.

A continuing process whereby an individual acquires a personal identity and learns the norms, values, behavior, and social skills appropriate to his or her social position (Dictionary.com).

→ socialize; → -tion.

To make social; make fit for life in companionship with others (Dictionary.com).

→ social; → -ize.

Of or pertaining to social groups, their activities, or to social relations.

From societ-, from → society, + → -al.

Hazâni, from hazân-, from hazâné, → society, + -i, → -al.

An organized group of persons associated together for scientific, cultural, or other purposes; e.g. a physical society. See also:
→ associate, → association, → dissociate, → dissociation, → social, → socialization, → socialize, → societal.

M.E., from O.Fr. societe, from L. societatem (nominative societas), from socius "companion," → associate.

Hazâné, from Av. hacenay- "getting together, association," from verb hac-, hax- "to associate, follow, accompany" (haxay-, hašy-, haš- "friend"), hacaiti "follows;" hacā "from, out of;" O.Pers. hacā "from" (Mid.Pers. hac "from;" Mod.Pers. az "from"); PIE base *sek^w- "to follow;" cf. Skt. sac- "to be associated or united with," sácate "accompanies, follows," sácā "with;" Gk. hepesthai "to follow;" L. sequi "to follow."

The science or study of the origin, development, organization, and functioning of human society; the science of the fundamental laws of social relations, institutions, etc. (Dictionary.com).

→ society; → -logy.

Of or pertaining to Socrates or his philosophy, followers, etc., → Socratic irony, → Socratic method.

Socrates (469?-399 B.C.), Athenian philosopher.

A means by which the pretended ignorance of a skillful questioner leads the person answering to expose his own ignorance (Collins).

→ Socratic; → irony.

The use of questions, as employed by Socrates, to develop a latent idea, as in the mind of a pupil, or to elicit admissions, as from an opponent, tending to establish a proposition (Dictionary.com).

→ Socratic; → method.

A metallic chemical element; symbol Na (L. natrium]. Atomic number 11; atomic weight 22.98977; melting point 97.81°C; boiling point 892.9°C; specific gravity 0.971 at 20°C. It was discovered in 1807 by the English chemist Humphry Davy from electrolysis of caustic soda (NaOH).

Sodium, from soda (NaOH).

The → sodium tail of the Moon as it appears in the sky opposite the Sun. The SMS undergoes changes in shape and brightness. It is brighter when the → new moon occurs at → perigee, when the new moon is north of the → ecliptic, and approximately five hours after the new moon.

→ sodium; → Moon; → spot.

1) A kind of → cometary tail appearing in some → comets, such as → Hale-Bopp. Sodium tails arise from the very strong → fluorescence of their sodium atom → D lines in the visible. They are rapidly accelerated to high velocities by the Sun, forming a very straight tail distinct from the → ion tail. The release mechanism of sodium from comets is still a matter of debate. Also called → neutral tail.
2) → sodium tail of the Moon.
3) A comet-like tail of Mercury similar to that of the Moon, but much longer, stretching up to 3.5 million km.

→ sodium; → tail.

A comet-like tail of the Moon comprised of → sodium (Na) atoms and invisible to the naked eye. The lunar surface is constantly bombarded by the → solar wind, → photons, and → meteoroids, which can liberate Na atoms from the → regolith. These atoms are subsequently accelerated by solar → radiation pressure to form a long comet-like tail opposite the Sun. Near → new moon, this diffuse cloud of Na atoms encounters the Earth's gravity and is "pinched" into a beam of enhanced density. This beam appears as the ~3° diameter Sodium Moon Spot (SMS) seen in the sky opposite the Sun. The spot is about five times the diameter of the → full moon, and is 50 times fainter than can be seen with the unaided eye. The spot is reflected light from millions of Na atoms that two days earlier were on the surface of the Moon. This spot is visible to sensitive cameras equipped with filters tuned to the orange light emitted by Na atoms near 589.3 nm (Baumgardner et al., 2021 Journal of Geophysical Research: Planets DOI: 10.1029/2020je006671).

→ sodium; → tail; → Moon.

General: Delicate in texture, grain, or fiber.
Not bright or glaring.
Physics: Of a beam of particles or electromagnetic radiation, having relatively low energy, as opposed to → hard. → soft X-rays

M.E. softe "yielding, gentle, mild;" O.E. softe "gentle, easy;" cf. O.S. safti, O.H.G. semfti, Ger. sanft, M.Du. sachte, Du. zacht.

Narm "soft; smooth; mild," from Mid.Pers. narm "soft; humble."

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy is smaller than the typical → kinetic energy of the relative motion of an incoming third body. See also → hard binary.

→ soft; → binary.

A member of a small class of objects which emit intense bursts of → gamma rays and → X-rays (> 100 keV) at irregular intervals. The bursts last for some 100 milli-seconds. It is conjectured that they are → magnetars. See also → starquake.

→ soft; → gamma rays; → repeater.

Same as → soft gamma repeater (SGR).

→ soft; → gamma ray; → repeater.